SPRING OPERATED SHOTGUN SPEED LOADER
A Thesis
Presented to the faculty of the Department of Mechanical Engineering
California State University, Sacramento
Submitted in partial satisfaction of the requirements for the degree of
MASTER OF SCIENCE
in
Mechanical Engineering
by
Kit Winslow Spelman
FALL 2015
© 2015
Kit Winslow Spelman
ALL RIGHTS RESERVED
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SPRING OPERATED SHOTGUN SPEED LOADER
A Thesis
by
Kit Winslow Spelman
Approved by:
______, Committee Chair Dr. Akihiko Kumagai
______, Second Reader Professor Kenneth Sprott
______Date
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Student: Kit Winslow Spelman
I certify that this student has met the requirements for format contained in the University format manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for the thesis.
______, Graduate Coordinator ______Dr. Akihiko Kumagai Date
Department of Mechanical Engineering
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Abstract
of
SPRING OPERATED SHOTGUN SPEED LOADER
by
Kit Winslow Spelman
Statement of Problem
To reload most modern day firearms a button is pressed to release the installed magazine and another magazine is inserted into the firearm. The second magazine has been preloaded with ammunition making the process quick and efficient way to reload a firearm. A shotgun does not have a detachable magazine which slows down the reloading process. Once all the ammunition from the shotgun‟s magazine has been depleted more shells are inserted through the loading port into the magazine one at a time. This process can take a long time since a shotgun can hold up to
(8) shells. If someone practices and practices they can become very efficient at reloading quickly but this process is still not as fast or efficient as a detachable magazine.
The purpose of this paper is to design a new invention that will auto feed shells into a shotgun quickly, and reliably as possible. This new design will be accomplished by designing a magazine re-loader that will house up to (8) shells. The shells will be pre-inserted into the loader ready for use. Once a shotgun is ready to be reloaded, this new loader will be held up to the loading port, activated by depressing a release button on the side, and a spring will load shells into the magazine of the shotgun. Since this method will be faster and more efficient that
v reloading shells by hand, this product will be more appropriately called a Spring Shotgun Speed
Loader or SSSL.
Conclusions Reached
The final design was not able to hold all (8) shells and keep the length of the SSSL a manageable size. The length of the final design is 35.33” long overall and can house up to (5) shells instead of the intended eight. Transferring all shells into a shotgun takes less than ½” second successfully and repeatedly. The goal was achieved in which the SSSL works and loads all (5) shells but the design could be improved to make the SSSL easier to use by shooter. A second iteration will come in the future that will address: ease of loading the shells into the loader, reduction of overall length and faster alignment to the shotgun.
______, Committee Chair Dr. Akihiko Kumagai
______Date
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TABLE OF CONTENTS Page
List of Tables ...... ix
List of Equations ...... x
List of Figures ...... xi
Chapter
1. INTRODUCTION ...... 1
Background ...... 1
Problem...... 2
Current Products ...... 3
Purpose ...... 6
2. CONCEPT PROTOTYPE ...... 7
3. SPRING FORCE DETERMINATION ...... 9
Why a Spring? ...... 9
Force Sensor Setup ...... 10
Force Sensor Measuremnt ...... 104
Spring Sourcing ...... 17
4. DESIGN ...... 20
Design Overview ...... 20
Shell Angle Determination ...... 20
Angle Shell Prototype ...... 33
SSSL Alignment ...... 34
Shell Opening Determination ...... 36
Push Button Release Design ...... 42 vii
Main Body Design ...... 44
Grip Design ...... 46
Pusher Design ...... 48
End Cover Plate and End Stopper Design ...... 50
5. FABRICATION ...... 53
6. TESTING ...... 58
Release Button Testing ...... 58
Pusher Testing ...... 60
Shell Loading ...... 63
Accidental Release Button Triggering Testing ...... 65
Spring Testing ...... 67
7. ANALYSIS OF THE DATA ...... 77
8. CONCLUSION ...... 81
Appendix A Individual Part drawings ...... 87
Appendix B Interlink Electronics FSR 402 Specifications ...... 93
Appendix C Arduino Specifications ...... 95
Appendix D Arduino Programming Code w/ 5 lbs. & 10 lbs. Verification ...... 96
Appendix E Shotgun 12 GA. Shell Measurements ...... 99
Bibliography ...... 100
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LIST OF TABLES
Tables Page
1. Force results from tests on loading shells...... 16
2. Testing springs specifications...... 70
3. Spring test loading data, original training shells...... 73
4. Spring test loading data, using new shells...... 76
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LIST OF EQUATIONS Equations Page
1. Voltage output equation...... 12
2. Newton to Grams to lbs conversions...... 13
3. Hooke‟s Law ...... 70
x
LIST OF FIGURES Figures Page
1. Parts of a shotgun...... 2
2. TEC Loader SL-12 Shotgun Speedloader...... 3
3. Arredondo Speedloader assist...... 5
4. Speedloader guide rod...... 6
5. Plastic tube prototype...... 7
6. FSR 402 schematic...... 11
7. Arduino Board Setup...... 11
8. Resistance vs. Force for FSR 402...... 12
9. Arduino verification setup, 5lbs...... 14
10. Arduino verification setup, 10lbs...... 15
11. FSR 402 sensor attached to a training shell...... 16
12. Overall exploded view and components of the SSSL...... 21
13. Maximum shell angle installed half way into magazine chamber...... 22
14. Minimum angle needed to install shell into magazine port...... 23
15. Shell straight line path clearance angle...... 24
16. Circular installation of shells, 10.25" diameter...... 26
17. Maximum shell circular pattern...... 28
18. Third model for shell loading angles...... 30
19. End resulting angle and curvature for shell entry...... 31
20. PLA plastic prototype of actual angle...... 34
21. Top section of speed loader...... 35
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22. Shell interference at curved section of SSSL...... 37
23. Shell clearance with 0.950" diameter tube opening...... 38
24. Maximum shell tolerance in 0.950" diameter tube opening...... 39
25. Maximum tube opening...... 40
26. Inside diameter 1.040" with maximum shell size...... 42
27. Release button...... 43
28. Push release button in depressed and blocking positions...... 44
29. Main body design...... 45
30. Main body cutout to locate grips...... 46
31. Left grip inside view...... 47
32. Right grip, outside (L) and inside (R) views...... 47
33. Pusher design...... 49
34. Section view of pusher and release button...... 50
35. End cover plate and main tube end design...... 51
36. End stopper design...... 52
37. Alignment T and coupler...... 54
38. SSSL fabricated design 1...... 55
39. Mounting plates on tested lower and mid body sections...... 57
40. Overall SSSL design for testing, 3/4" PVC lower shown...... 57
41. Redesigned release button in blocking and release positions...... 59
42. Release button redesign (left), new third design (right)...... 60
43. Pusher design evolution...... 61
44. Spring end types...... 62
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45. Examples of different positions of the spring end...... 63
46. Install tool (Left), tool installed on Arredondo handle (Right)...... 64
47. Tested springs inside the SSSL...... 69
48. Spring #1 with broken pusher...... 71
49. New and deformed shotgun shells...... 75
50. Pusher jammed in loading port on loading ramp...... 79
51. Final design and overall views of SSSL...... 80
52. New design of pusher to try on next iteration...... 85
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1
1. INTRODUCTION
Background
In any competition that involves time, speed plays a big factor in winning and losing no matter which sport is involved. One such sport activity is 3-Gun Competition shooting, which is held around the country. In 3-Gun Competition shooters will use a pistol, rifle and a shotgun to hit targets in various stages. Each stage has different setups for targets, cover spots, and rules to follow which informs the user which firearm is used in which stage.
In 3-Gun Competition speed is one of the biggest factors to be a top contender.
To calculate the total score a tally of the times at each stage is added with any penalties which incurred adding more time to that stage (Tap Rack Bang Creative). Each stage‟s time is added together and the person with the lowest total time determines the winner for the match. During each stage the competitor will have to aim from multiple positions, walk from cover position to cover position and reload quickly to help achieve the best possible overall time and score. One of the slowest performers during reloading in this competition is the shotgun.
Unlike pistols and rifles, shotguns carry their ammunition inside the firearm not in a removable magazine that is preloaded being put into the firearm, shown in Figure 1
(Coustan, 2005). Once the shotgun is empty, the operator will manually input shells, one at a time, into the magazine loading port to reload. The magazine is a tube that houses up to (8) shells but there are shorter magazines which will hold fewer shells. The magazine is directly underneath the barrel and is attached to the receiver. Instead of quickly
2 releasing an empty magazine and inserting another magazine that is fully preloaded, a shotgun is reloaded a shell at a time. This manual labor costs precious time in a competition. There are different types of shotguns but this paper will focus on semi- automatic and pump action types that have the magazine directly below the barrel and attached to the receiver.
Figure 1 Parts of a shotgun.
Problem
Normally shells are inserted into the loading port one at a time, which is a very good method in standard conditions. In a competition this is very inefficient and can cost the competitor the win in a match. The purpose of this paper is to develop a new invention that can reload multiple shells at once that will perform the action faster than a human can manually inputs the shells into a shotgun. The best scenario is to load (8) shells at once into the shotgun, since that is the maximum amount a shotgun can hold in the magazine.
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Current Products
There is currently one product that can be purchased on the market called the TEC
Loader SL-12 Shotgun Speedloader (Speedshooter.com). This kit comes with a little pouch, two TEC loaders, and a mounting bracket which sells for about $59.95 shown in
Figure 2. Each TEC loader is a rail that can be preloaded with up to (4) shells on it, and then put into the pouch for use. Once the shotgun is empty the shotgun is turned over, a preloaded rail from the pouch is inserted it into the entrance of the loading port, and the lever that is attached to the rail is moved forward. This lever pushes the shells into the shotgun magazine. In order to load all eight shells the process has to be repeated.
Figure 2 TEC Loader SL-12 Shotgun Speedloader.
There are many reviews and videos online of current owners talking about the TEC product. Most of the reviews say that the product works part of the time and if the rail is not exactly lined up correctly with the magazine entrance the shells cannot be inserted.
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Other reviews mention that if there is any misaligned, the shells will fly out on the ground instead of going inside the magazine. Other problems with this product are the shells can potentially fall out of the rails if bumped or hit while in the pouch. Many reviews say it takes a lot of practice to know exactly how to use it effectively. Reviewers also say if someone takes their time and line everything up this works well, but not made to be used is they are in a hurry, so it would not be ideal for competition use
(Shotgunworld.com).
To solve the issue of misalignment a Speed Loader Assist has been created by
Arredondo. This assist is permanently attached to the outside frame of the shotgun shown in Figure 3 (Speedloaderassist). The assist is curved on the inside to match the curve of a rail and help guide the TEC loader up into position for reloading. This does actually help a lot when quickly reloading but does come with a heavy price tag of
$157.45. Jerry Miculek is a professional speed/competition shooter and has this mounted on his shotgun. He can easily fire (7) shots that are preloaded in his shotgun then reload using this speed assist and TEC speed loader in 3.5 seconds shown in this video link. https://www.youtube.com/watch?v=xXkyEbrqNGw
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Figure 3 Arredondo Speedloader assist.
Another problem with the TEC loader is that the inner rail that propels the shells forward can be misaligned internally. This causes the end that moves forward to change angles and not work properly. To solve this problem a guide rod has been made to keep everything in line shown in Figure 4 (Speedloaderrod). The rod works but is another addition someone would have to purchase and install. If a user did not know about this, they also may have issues while trying to reload.
Just recently a (6) shell speed loader has come out on the market to purchase from the same company as the TEC Speed Loader Assistant. This new six shell loader is all aluminum instead of plastic which makes it more durable, but does increase the cost.
This, just like the plastic loader, the aluminum does not fit inside the loading chamber so the alignment and feeding of the shells can cause problems. The aluminum one does not need the guide rod which saves money and the handle has a better feel when gripping.
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Figure 4 Speedloader guide rod.
Purpose
The purpose of this paper is to develop a new invention that can reload multiple shells at once that will perform the action of loading the shells into a shotgun faster than a human can manually. The current products both need the shooter to move the handle to insert the shells into the shotgun. This new invention will be able to hold the same amount or more shells than the current product. The goal is to load up to (8) shells at once into the shotgun, since that is the maximum amount a shotgun can hold in the magazine. The new invention will perform the reloading process faster than a human can reload. To achieve this faster reloading process a spring will be used to assist the shells into the shotgun. This product will be more appropriately called from now on a Spring
Shotgun Speed Loader or SSSL.
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2. CONCEPT PROTOTYPE
Before beginning the design, a concept and prototype was made. This simple prototype was made of a clear plastic tube 1-1/8” outside diameter tube that is hollow with an inside diameter of 1”. This type of tube can be purchased at any local hardware store. The end upper ¾” of the tube was cut 3” from the end. This cut allowed the tube to be placed flush up against the bottom of the loading port. The tube had to be curved downward out of the way of the trigger guard so two vertical cuts were placed at the end of the upper ¾” cut to allow it to curve. Training shells where then placed inside the tube and pushed up into the loading port by hand to see if the concept was feasible, shown in
Figure 5. The concept and prototype was a success. By placing two shells into the plastic tube and used a third to force them forward, the first shell easily goes into the shotgun loading chamber. Using a fourth shell can force the second shell in to the shotgun chamber.
Figure 5 Plastic tube prototype.
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It is to be noted that during all testing training shells were used. Training shells are the same length as actual shells, they are weighted to feel the exact as actual shells but they have no primer in the end. The primer is replaced with a plastic insert so they cannot be fired. All most all live 12 gauge shotgun shells have the outer plastic coating color as red, with a few exceptions of pink, 20 gauge shells are yellow, 16 gauge are purple. Training shells have the outer plastic as a neon green to help easily recognize they are not actual ammunition and cannot be fired.
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3. SPRING FORCE DETERMINATION
Why a Spring?
There were many obstacles to overtake when designing a new speed loader. The first was to try and eliminate as much human interaction as possible. Reducing human interface reduces the chances of them doing something incorrectly. This reduction of human interface was done by having a mechanism do the work which will be more repeatable, reproducible and more dependable. Using a mechanism sized and designed properly can react faster than a most humans. Operators of the shotgun will have to bring a loader up to the shotgun for reloading, no matter which speed loader is used, so that cannot be eliminated. What changed was how the shells are driven into the magazine chamber. With the TEC loader the human drives the shells into the shotgun, for the SSSL design it was designed to use a spring to force the shells up into the compartment. A spring when compressed contains static inertia waiting to be released. Once the spring is able to expand, the rate at which it moves is faster than most people can move their hand, which in turn will be faster at reloading (White, 1966).
Now that a spring was chosen to be used the sizing of the spring was determined.
There is a spring that resides inside all shotgun magazines and is compressed when shells are inserted. Once a shell is ejected from the firing chamber the force of the compressed magazine spring forces the next shell into the chamber. The main spring inside the SSSL needed to be sized such that its force when fully extended was greater than the force of the compressed spring inside the shotgun magazine. If the main spring inside the SSSL
10 when fully extended had a force less than the force of the magazine spring, the shells will not be driven up into the magazine chamber.
Force Sensor Setup
To size the main spring, the force required to push the last shell inside the loading chamber needed to be obtained. In order to obtain this end force of the main spring,
F_ems, the force required to insert the eighth shell needed to be found, F_8s. To calculate the F_8s value, a force sensor, model FSR 402 from Interlink Electronics, was used; specifications of this sensor are located in the Appendix B. This sensor was chosen because it can detect forces from 0.1N to 100N, and it had a diameter of 0.73”, which size fits on the end of the shell without any overhang.
A simple electronics device, Arduino 16 Hz board, was setup to measure and record the values of the FSR 402, the specifications are located in Appendix C. This setup allowed pressure to be applied to the FSR 402 and output a voltage to the Arduino board. The wiring schematic for the FSR 402 is shown in Figure 6.
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Figure 6 FSR 402 schematic.
For verification of testing and data collection a 10k ohm resistor was used in the
RM position of the schematic and the actual setup is shown in Figure 7.
Figure 7 Arduino Board Setup.
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The Arduino board was then programmed to convert the input voltage to find resistance of the sensor using Equation 1, where Rfsr is the resistance of the FSR 402,
Rm is the 10k ohm resistor, V is the voltage input 5 Volts, and Vout is the output in volts.
Once the resistance of the FSR 402 is obtained the force, in grams, can be found using
Figure 8.
(1)
Equation 1. Voltage output equation.
Figure 8 Resistance vs. Force for FSR 402.
Equation 1 was input into the programming of the Arduino, the output value was displayed in Newton‟s which was converted to grams to be able to use the chart in
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Figure 8. The resistance chart was used to approximate the force in grams in the programming of the Arduino board.
Arduino has a big user follow group who post findings and programming codes.
A programming code was found on a posting for a similar resistor and was downloaded for this application. The code was then modified for this specific sensor and then converted from grams to pounds. Pounds is used specify a spring for sizing, so the conversion to pounds needed to be done. Equation 2 has the conversions from Newton‟s to grams and grams to pounds. The values of the chart are an approximation so a test was performed to ensure the values were correct coming from the program code. The programming code for the Arduino board is located in the Appendix D, which displays the code on the left side and the verification of the weight for the right side for both 5 lbs. and 10 lbs. weights.
(2) Equation 2 Newton to Grams to lbs conversions.
To verify that the setup of the circuit board and the program was correct a known weight of 5lbs and a 10lbs weight were used. The setup for the verification of the program is shown in Figure 9 and Figure 10.
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Figure 9 Arduino verification setup, 5lbs.
The program was modified with some small adjustments to the numbers in the code from the approximation of the chart to obtain readouts of correct weight 5lbs. and
10lbs. thus verifying the program was correct. With the program correct, the force sensor was then attached to the end of a training shell shown in Figure 11.
Force Sensor Measurement
The FSR 402 sensor was attached to the end of the shell since that is where the force is being applied to insert the shell into the magazine chamber. Three trials of sensor readouts were run to test the force at different shell positions as they were loaded.
Test A had an empty magazine compartment so the sensor was on the first shell being input, Test B the sensor was on the fifth shell being loaded and Test C the sensor was on the eighth shell being loaded. Each of these tests were performed (10) times to
15 verify the force and get the average results of the force. The different positions will determine if more force was needed to push all eight shells in or if the force remains constant. The results for each test are shown in Table 1. The readings from the FSR 402 sensor was displayed and recorded every 0.125 seconds. The highest value during the install of the shell was recorded in the chart shown in Table 1.
Figure 10 Arduino verification setup, 10lbs.
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Figure 11 FSR 402 sensor attached to a training shell.
Table 1 Force results from tests on loading shells.
The results from the tests show that as more shells are being input into the shotgun more force was required to install the next shell. This makes logical sense because of the spring in the magazine chamber, as more shells were input the spring compressed and the force increased due to the compression of the spring. The force did not change much from the first to the eighth shell being installed, a 7 pound difference between the maximum recordings. The maximum amount of force measured for the
17 eighth shell was 30 pounds so using a factor of safety of 1.333 gives a spring force needed of 40 lbs.
Now knowing that the force of the spring needed to push the last shell into the shotgun is 40lbs, a spring was chosen such that it would meet this requirement. The spring was sized so that in the full extension inside the speed loader the force being applied would be 40 lbs.
Spring Sourcing
Three spring manufacturing companies were contacted to help specify a spring to meet the requirements; www.springsfast.com, www.americanprecspring.com, and www.mwspring.com. The spring requirements were that the outside diameter was no bigger than 1”, at the maximum length of 31” the spring needs to have a force of 40 lbs., and the spring must compress to 12”. The 12” compressed is the total length 31” minus the shells in loading position, minus 0.62” for the pusher. The 12” length is roughly 1/3 of the overall length. The second and third companies contacted both said that they were not able to design a spring with the requirements. The first company said the same problem but wanted to work for another solution to be able to work in the application.
The reason why the requirements would not work was that in a compressed state, no matter the material or wire diameter, the tensile strength when compressed is above the yield strength of the wire material causing it to fail. The options to make a feasible part were to increase the outside coil diameter and thickness of wire, or to increase the
18 compressed length. Since the outside diameter of the tube was fixed, it should be roughly the same size as the shell; the compressed length was the only option to change.
The new resulting spring that would meet the initial requirements had 1” outside diameter, force of 40 lbs. at the 36” length, 0.120” wire diameter, and 52.22” long in free length with 179.3 active coils. This meant the spring would be compressed 16.22” to get inside the loader, assuming a 36” long loader, and then compress another 18.88” to have all eight shells loaded.
The length of the SSSL could then be calculated knowing how long the main spring would be in the compressed state. For (8) shells, each being 2.36” long, the length of all shells is 18.88” long. The first shell would be inside the loader as well, and was set back 4.5” from the tip of the SSSL. The length of the compressed spring that was behind the eighth shell is 23.38” long, so the total length of the SSSL was to be 46.76”.
There were two problems with the SSSL being that long. A shotgun speed loader normally is carried in a pouch located on the side of the hip of the shooter. Anywhere from one to eight speed loaders can be in the pouch. Having a loader that‟s almost four feet long on someone‟s hip will not work, especially if the person is shorter, the loader would drag on the ground. A length of 24” would be the longest someone would want to be able to carry on their side but ideally it should be shorter. The second problem with this was the force it took to compress the spring to the compressed „ready‟ length. The force required to compress the eighth shell would be 74.18 pounds of force. The average person would not be able to compress the spring and even if they could, to do this repeatedly, would be even harder.
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The only option to make a loader for everyone was to reduce the number of shells which reduces the length of the SSSL. By reducing the shells the loading force needed for the last shell decreased as well as the compressed length of the spring. Since the TEC speed loader holds four shells, the SSSL was designed to hold four shells as well. This would be equivalent for the amount being loaded to compare for a side by side comparison in the future or by customers.
The company, www.springsfast.com, was contacted again with the new requirements of a force of 30 lbs. and a new length of 24” overall unit length. The 30 lbs. came from the testing at the 5th shell. Again the requirements could not be designed; if the length was increase to 40” the spring could be designed. This 40” length would have to work but was longer than the desired 24” length. The new size of the spring was
50.21” free length, 15 lbs. at the 40” length, 0.875” outside diameter, 0.110” wire diameter and 200 active coils. At the compressed length of 12”, length of (4) shells, it would take 41 lbs. of force to compress. This was still higher than desired but more manageable and could be done.
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4. DESIGN
Design Overview
The design for a new spring activated shotgun speed loader has many components that needed to be designed. These components all needed to be sized appropriately so that when they are installed together they work properly and have appropriate clearances.
The SSSL design has ten major components used to complete the new product which are: shell angle from loader to shotgun, opening of loader tube for shells to travel, main body top section, main body mid/lower section, left grip, right grip, release button, pusher, end cover plate, and main spring. All of these components can be seen in the exploded view in Figure 12 and how they all fit together. The main body, #1, is all one piece but the designing of it was broken into two sets: top section and lower section.
Shell Angle Determination
The biggest hurdle to overcome for a speed loader was the angle at which the shells were being inserted into the shotgun itself. The loading port which shells are loaded into is located up and inside the frame, so the shells needed to be inserted at an angle to reach the main insertion point for the magazine chamber and then travel parallel to the shotgun to finish being installed. The clearance of the magazine chamber is only
0.030” bigger than the shell itself; which does not allow for much misalignment when feeding shells in the shotgun. On the outside of the loading port there is a loading ramp that has a spring behind it. In normal position the ramp is down so that the loading port opening into the magazine is not visible. Pressing the loading ramp up, it pivots on the
21 back towards the butt stock, and the loading port chamber becomes visible. The ramp creates an angle to allow the shells into the loading port chamber. The angle created by the ramp is not the „ideal‟ angle for insertion but helps the user guide the shells into the loading port.
Figure 12 Overall exploded view and components of the SSSL.
The TEC Loader has a very small end goes into the loading port and presses the loading ramp out of the way. When using the TEC loader there is no support for the shells once they are in the loading port. The force of pressing all the shells at once in a quick motion keeps the shells in a line as they travel into the magazine chamber. If the end of the TEC loader is not fully engaged with the loading ramp the angle will not be set
22 correctly and the shells will not be able to be inserted in the magazine. The other issue with the TEC loader is if the motion is not consistent in pressure and along a consistent path the shells will not be inserted into the magazine. These two potential issues are some shortcomings of using the TEC loader which lead to failed installations of shells.
The correct angle, path and speed are critical to get an accurate and repeatable reload.
To make sure the SSSL had the proper angle and path for loading shells, several model designs were investigated. The shotgun frame, loading ramp and magazine chamber were modeled in SolidWorks 2013 along with a shell to accurately find the proper angle. A shell needed to be installed at an angle to fit inside the chamber as shown in Figure 13. The maximum angle at which the shell could be installed half way into the chamber is at roughly 5.23 degrees.
Figure 13 Maximum shell angle installed half way into magazine chamber.
The angle at which the shells could be started into the end of the magazine is more than the 5.23 degrees but needed to make sure that the second shell cleared the
23 loading port, loading ramp and trigger guard/frame. An angle of 15 degrees is depicted in Figure 14, which represents the biggest angle a shell could be started to be installed before it hits the loading port and magazine wall. This figure shows that the first shell being inserted into the loading chamber is touching the top of the magazine wall, outside face of the loading port and the back frame hits the second shell. The problem with this was that the two shells are not in a line with each other so the paths they are traveling was not the same, which does not help giving a smooth path for the shells to travel.
Figure 14 Minimum angle needed to install shell into magazine port.
Ideally all shells should be aligned and follow the same path to achieve the smoothest and quickest installation for reloading. The angle at which all shells were in a line and would clear the frame was investigated next. The angle for this was 24.26 degrees which is shown in Figure 15. The path was ideal for the shells, all being in a
24 straight line. Looking at the end of the first shell, the one about to be installed into the magazine, it would not work. The angle was too great and the shell would not fit into the magazine. Thus the shells cannot be installed in a straight line into the magazine. A curvature would be needed for the shells to follow which would allow them to enter the magazine without binding on the magazine walls and loading port face.
Figure 15 Shell straight line path clearance angle.
A circle could resolve the improper angle for loading the shells to allow them to enter the magazine chamber smoothly. Various diameters of circles were investigated and drawn to find one that could potentially work. The main diameter about the shell rotation was drawn so that it would represent the centerline of the shell‟s path to follow.
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A shell was then inserted into the magazine at an angle so that it could easily be installed and a circle was drawn around the end point of the shell. An axis was created at the center of the circle and the shells were patterned about the axis so that the end of one shell would touch the beginning of another. One scenario examined had diameter of the circle of 10.25” which could work shown in Figure 16.
The path shown in Figure 16 could work for the shell installation but another item needed to be investigated for this scenario, which was the angle of shell to shell contact.
The force being applied was at the trailing edge of the shell pushing towards the frame.
If there was a force pressing at the end of the second shell at the bottom corner parallel to the shell‟s centerline, all the force would be put into the single point at which it touches the shell above it. The next shell was not at the same angle so the force being applied to it was broken into force vectors, X1 in the x-direction and Y1 in the y-direction. The angle between the two shells in addition with the angle Ɵ1, would help determine the amount of force in each direction. In this case the Ɵ1 was roughly 40 degrees so the force would be applied more in the x-direction that the y-direction. This was not ideal since the shells were to move up into the loading port, which is in the y-direction. To move the shell in y-direction with an angle as shown, more force would be needed to get the shell to move in the vertical direction. The bigger the angle between the shells traveling in the same direction the less force needed to have them move along that path. In other words more parallel the shells the easier they to move in the desired direction (Beatty, 2006).
Another consideration was looking at the force that was being applied to the very outer point of the shell casing relative to its center of gravity. If the force was applied at
26 the bottom corner that shell would want to pivot and rotate in a clockwise motion about that contact point, assuming it was not constrained. This would cause the shells to follow an inconsistent path and produce improper feeds. This rotation was prevented and addressed further in the paper by the opening of the shell tube.
Figure 16 Circular installation of shells, 10.25" diameter.
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The angle Ɵ2 was ideal between the first shell being installed and the second shell because this theta angle was small. The small angle transfers the most amount of force in the x-direction allowing the shell move easily in that direction to be installed into the magazine chamber.
The result of the model in Figure 16 found the shells that were the furthest away from the loading port should be as parallel with each other as possible, which generated the maximum amount of force in the direction the force was being applied. The greater the angle between the two shells, up to 180 degrees, increased the amount of surface contact area from one shell to the next for the force to be applied. The opposite showed that the smaller the angle between shells, the less contact area for the transfer of force in the direction desired, which was not desired in the vertical direction.
The contact area was importance because it would provide a consistent and uniform direction of motion transferring from one shell to the next. The more contact area the better, which prevented the next shell from unwanted movement. The least amount of contact area allowed the shell being pushed freedom to move/pivot about the contact position. Having the force applied towards the center of the next shell also helped move the shell in a straight line preventing it from rotating while being pushed (Likins,
1973).
Lastly the first circular angle shell investigation found the smaller the angle between the very first shell and the second shell into the chamber was ideal to get the maximum amount of force in the x-direction to install the shells.
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A bigger diameter of a circular path of motion was also investigated. The bigger diameter allowed the shells to follow a more inline path shown in Figure 17 and reduce the angle between them. This bigger diameter showed that the shells were becoming more in line with each other, which was the purpose for the examinations of the angles.
The angle between the third shell and second shell was closer to parallel while the angle
Ɵ3 was smaller which was good for this scenario because the shells needed to move in the x-direction to reach the magazine chamber. The Ɵ4 was closer to the same angle as
Ɵ3 than the angles between Ɵ1 and Ɵ2 in the previous example, which confirmed the shells were becoming more in a line. The diameter of the centerline of the shells is shown in Figure 17 which was 12.43”.
Figure 17 Maximum shell circular pattern.
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The shells in Figure 17 had a circular path drawn on the outside to check that outside casing of the shell would not hit the frame or the loading port. This scenario also displayed that the shells were pushing on the next shell more towards the center of that shell which reduced the amount of the individual shell rotation. The downside to this scenario was that the shells were slightly rotated about their own center of gravity, so the area that they occupied was more than if they were in a straight line. This was due to the circular pattern of the angle from the first shell being installed. Changing the angle of the first shell would change the angle of the patterned shells. The result from this model was that a bigger diameter helps reduce angle between shells and moves the contact point between shells towards the center with more surface contact.
In order for one shell to follow the path of the shell in front of it, while making sure it was not rotating about its center of gravity, a third model was created. This third model used a similar diameter as the first model but the angles of the shells were changed about their center of gravity shown in Figure 18. This new angle allowed the previous shell to touch the next shell closer to the center of the shell. The angles between any two shells were closer to 180 degrees which was good for the vertical shells. The contact points between shells were closer to the centerline compared to the first two models which would provide a more linear movement. This allowed for a better force translation between shells and minimizing the angle of rotation between shells.
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Figure 18 Third model for shell loading angles.
The third model created promising results for the angle into the magazine; the lines of the inner blue circle end right at the back of the magazine chamber. The downside was outer blue circle, which represented the path of the shell casing, still interfered with the frame just behind the loading port, so that needed to be resolved. The shells were not inline, to get the best transfer of force between shells they were to be flat up against one another, so another room for improvement.
To correct the force transfer to be flat against the next shell, a partial circle would be used instead of an entire circle for the path to follow. The first and second shell going into the loading port remained the same as the third model and instead of the third and fourth shell following a curve they came out linearly behind the second shell.
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This new model was tested with a couple variations of having the shells come out straight out the end of the second shell. There was some adjusting of the angle to clear the frame and diameter of the circle to optimize the results. The final result of a new angle of 37.71 degrees and radius of 4.43” were obtained and shown in Figure 19.
Figure 19 End resulting angle and curvature for shell entry.
The blue lines around the shell again represent the outer most part of the shell casing. There also needed to be a gap between the shotgun frame and the shell because the SSSL tube would have a wall thickness that goes in this region, which was considered during the design. The second shells end was touching the loading ramp, which was used to assist the shell to change directions from the 31.74 degree angle to a horizontal position. The radius of the center of the shell path changed from the previous models as
32 well. Only a single shell needed to rotate 31.74 degrees so a smaller radius was used in the transition. The rotation of the shell takes place entirely inside the loading port region which saves room in the SSSL profile. At the intersection of the center line about the first shell and the start of the magazine chamber the blue line was drawn tangent to the horizontal axis, so the shells would be lined up going into the magazine chamber minimizing any chance of misalignment one way or another.
The centerline of the vertical shells were not tangent to the centerline of the left end of the radius centerline, shown in Figure 19. This was drawn a couple different ways before this solution was determined. Having the radius tangent to the straight lines did one or both of two things. The first was if the straight shell remained in the same position but the radius changed this moved the tangent position, it pushed the radius farther into the loading port and the angle became too tight for a shell to follow in that region. The other result was if the radius remained where it was shown but the straight shell line was moved to become tangent. This changed the angle of the straight line of shells to a bigger angle, so they were farther from the frame. Having the shells farther from the frame was not a bad thing but made the SSSL profile a little longer, which the length was trying to be reduced as much as possible. By having the angle not tangent the shell gave more room inside the loading port to rotate the shell to the correct position before entering the magazine. The shell could float freely in the loading port and adjust as necessary to have the shell behind it make contact in the best possible fashion.
While creating the last and final model of the angle the actual shotgun and shells were used and studied to help approximate the angle. By loading a shell by hand
33 repeatedly it became apparent that the shells did need to follow a curved path at the loading port to be guided into the magazine. Although measurements could not be taken since the shells were inside the loading port and could not be reached, the testing by hand showed a visual representation and assisted in the development of the model.
The actual body of the SSSL would not go inside the blue sketched region that is inside the loading port shown in Figure 19; the body of the SSSL would mimic the sketched shape on the underside of the frame beneath the loading port and cover the sides of the frame. This shape would help guide the bottom side of the shell into the magazine in the constant path unlike the TEC loader where there is nothing there to support and guidance of the shells.
Angle Shell Prototype
Now that an accurate model for the SSSL angle was determined a test model was fabricated to verify that it was correct. A small section of the angle was fabricated using a 3D printer out of PLA material. This test part had the exact same profile as the final angle sketched model and the part can be seen in Figure 20. The test model could hold one and a half shells but it was only to verify that the shells could easily be pushed into the magazine. Placing two shells into the test part and using a finger to push them forward, the first shell starts into the chamber with great ease. Using a third shell to push behind the second shell, the first shell completely entered the magazine. By repeating the steps with another shell the second shell was inserted into the magazine. This test was a
34 success and verified that the angle was correct and would work for the design of the
SSSL.
Figure 20 PLA plastic prototype of actual angle.
SSSL Alignment
Now that the angle of the loader has been determined, the alignment of the SSSL with the loading port was designed. The TEC loader was very narrow and had room between it and each wall of the loading port even when centered. To eliminate this, the
SSSL was designed wider for less play when inserted into the port region, shown by label
C of Figure 21. The width of the SSSL was wider than the frame of the shotgun so that when positioned up against the frame, it would surround both sides of the frame for alignment. The SSSL incorporated flat edges on the top inside face that touch the bottom of the shotgun frame to provide consistent alignment vertically when installed every time label B of Figure 21. Along the back top portion a flat surface a notch was designed to a
35 set the height, so that when the SSSL was inserted in the loading port the flat edges would stop against the bottom of the shotgun frame, thus positioning it at correct height shown by label A of Figure 21.
At the front end of the SSSL, where the shells come out, a lip was incorporated so the lip fits up inside the loading port shown by label D of Figure 21. When the SSSL is positioned this lip would be up against the frame where shells are inserted. This would prevent someone from trying to insert the SSSL too far forward into the loading port and give the operator a stopping point of when the SSSL was properly in place ready to insert the shells.
Figure 21 Top section of speed loader.
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Shell Opening Determination
Once the position and angle of the SSSL were obtained the actual opening for the shells to travel was investigated and determined. The outside diameter of an average 12
GA. shell on the brass end was found to be 0.878” which was bigger than the plastic coated section. Appendix E displays a table with all the recordings of the shells taken to obtain the average, min and maximum values of the brass end. These were needed because the tolerances were not specified and controlled by the manufacture. In order for the shells to travel freely the center opening of the SSSL needed to be bigger than this brass diameter. There were two areas to consider determining proper size of opening; the first was the straight part of the tube and the second was the region that curves where the shells enter the loading chamber.
The easiest and most straight forward opening size was the straight section of tube. The shells all travel in a straight line so the opening could be just bigger than the shell itself. An opening with 0.900” would work assuming everything was made and aligned perfectly, that give a clearance of only 0.022”, which in manufacturing is difficult to hold for plastic injection pieces. To consider tolerance for plastic injection the opening was designed at 0.940” which yields a clearance of 0.062”. This was chosen because of tolerance for plastic injection can maintain a tolerance of 0.040” and the tolerance of the shell to be 0.015”. If the injection mold was under by 0.040” and the shell was over by
0.015” the stack up would yield a result of 0.007” gap that the shell could still fit and slide in.
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The second section for the tube opening was for the curved section. The shell would travel in an arc motion when traveling at the end of the SSSL into the loading chamber. When the shell travels in the area of the curvature its displacement of area is wider that the diameter of the shell in a straight line. The peaks of the front and back shell would interfere with the inside walls of the SSSL if the opening at the curved section had the same diameter as the straight section, shown in Figure 22.
Figure 22 Shell interference at curved section of SSSL.
To overcome this possible interference the inside diameter of the path needed to be bigger so that the shell would be able to travel in the arc motion. Since the straight section of the tube had a diameter of 0.940” that was the first diameter investigated, which was shown in Figure 22 the curved diameter would need to be bigger. This diameter was too small and the shell interfered with the walls by about 0.006”. The next
38 investigated diameter was 0.950” which is shown in Figure 23, which the shell should clear because of the 0.010” increase and only 0.006” interference.
The shell had enough clearance to transition from straight to a curve to enter the loading chamber without having interference or jamming in the tube. Again this was assuming everything was made exactly to drawn size with nominal values. With the opening of 0.950” the clearance on each side was roughly 0.003” which was not a lot of room for error. The tolerance maintained by the manufactures of shells was not known so it would have to be approximated. Using the measured shells which varied 0.008” from min to max, an assumed tolerance of +/- 0.015” was used. A new model of the shell was drawn with an outside diameter of 0.895” to represent the maximum diameter that a shell would have. This was then modeled into the same tube opening of 0.950” diameter shown in Figure 24.
Figure 23 Shell clearance with 0.950" diameter tube opening.
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In such a case that the tube was made perfect but the shell was at the upper end of its tolerance the tube having a diameter of 0.950” would not allow the shell to pass into the loading chamber. Again the diameter of the tube opening would need to be increased to allow for the tolerance stack up.
Figure 24 Maximum shell tolerance in 0.950" diameter tube opening.
The opening was increased to the maximum amount at the current angle which has a diameter of 1.20” which is shown in Figure 25. This image shows that if the diameter of the tube increased any more the outside of the tube would interfere with the trigger guard. Once the tube hits the trigger guard the angle of the tube would change, which was not a viable option.
At the maximum tube diameter of 1.20” the tube opening would allow for the
SSSL to have the inside opening shrink the maximum amount and have the shell be at its upper most tolerance and allow the shell to travel freely, so why was this not ideal?
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Having a too big of tolerance was not ideal because this allowed the shell to wobble and be moved at an angle inside the tube which is shown in Figure 25.
Figure 25 Maximum tube opening.
Once the shell was at an angle it would take more force to push it out of the SSSL because the edges of the shell will be creating friction along the inside tube face and it will not want to travel in a straight path. The shell behind the shown angled shell would be touching it at a single point so the force to move the anlged shell along the designed path greatly increases at that point, as opposed to having a contact with the entire face; these same issues were discussed in the angle investigation. Another issue was if the shell angles was too much the shell may become wedged inside the tube. In the Figure 25 the shell has an angle of 10.2 degrees off its center which was too much to travel along the path with minimal effort of force from a shell behind it. This could jam the shell in the tube or in the loading port during the unloading process preventing the SSSL from operating properly (Fowles & Cassiday, 1999).
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Since a diameter of 1.20” was too big and 0.950” was too small a medium value needed to be determined. The middle value between the two is 1.075” but this should not be chosen simply because it was in the middle. Consideration of tolerance for both the shell and the SSSL at their peak values needed to be taken into consideration as well as minimizing the clearance and room for play around the shell inside the tube.
The inside tube diameter was gradually increased from 0.950” until a proper clearance of 0.020” was found at tolerance stack up. The shell with the upper tolerance model was used and a 0.020” clearance on both sides of the shell to travel was used. This extra clearance would allow for any lower end tolerance of the SSSL. This also would not allow any harsh angle of the shell inside the tube. With an average diameter shell of
0.878” the clearance was increased even more which allowed for more tolerance of the
SSSL. This was good because more often than not plastic injection mold parts tend to shrink more that designed, which means the parts are on the small end of the tolerance, rather than on the upper end of the tolerance.
The biggest clearance that a shell would need for the curve would be 0.895” max shell size, plus 0.025” tolerance which gives 0.920”. To calculate the clearance for the curve, the shell clearance of 0.920” was added to 0.020” clearance around the shell, plus
0.040” the plastic potential shrinkage on each side, which yields 1.040” the clearance of the curve. This inside diameter of 1.040” was used to design the SSSL which is shown in
Figure 26.
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Figure 26 Inside diameter 1.040" with maximum shell size.
Push Button Release Design
After the designing the tube other minor issues came along. One such issue was when shells were inserted into the SSSL; the main spring was compressed and wanted to expand back to the normal extended position. This was not desired, once the shells were inserted they should remain in the ready position until the SSSL is ready to use. A stopper was added near the top of the SSSL in the handle portion. This stopper prevented the shells from coming out of the SSSL by staying in the path of the shells. In order to release the shells, the stopper needed to move out of the way. Thus the stopper was transformed into a push button release shown in Figure 27.
To keep the push button release in the path of the shells a secondary smaller spring behind the push button body was introduced. The secondary spring was located near the top of the tube perpendicular to the tube so that the force of the secondary spring
43 forced the push button into the shell path. Once the SSSL was ready to release shells, depressing the push button release moved the release button body out of the path of the shells and compressed the smaller spring, thus releasing the main spring forcing the shells out of the SSSL. To reduce the overall width of the SSSL a cavity was created on the left side of the main body of the release button for the smaller spring to fit inside.
Figure 27 Release button.
In the normal position the top “hat” part of the push button would be in the opening of the tube, in the path of the shells, to prevent them from ejecting at the wrong time. The underside of the top “hat” needed a cut out in it, once the button was depressed, this cut would allow the “t” of the pusher to pass. Both the depressed position, left image and blocking position, right image are shown in Figure 28. This push button was designed to only have to move 0.445” from ready “out” position to depressed position which cleared the path of the shells.
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Figure 28 Push release button in depressed and blocking positions.
The release button needed to be secure and stable so housing was designed to keep it in position. The housing was located on each of the left and right grips by adding ribs to the inside walls. These ribs would prevent the release button from moving left, right and down when viewing the release button from the open end where the smaller spring enters the release button.
Main Body Design
The main body of the SSSL was designed in a circular fashion since the shells are round. The upper part of the main body housed the opening of the tube, as discussed earlier which touches the frame of the shotgun, used for alignment and where the shells come out. The alignment section is labeled A in the region in Figure 29. Along the entire bottom of the circular body an upside down “t” profile was cut which the pusher follows was designed next. In the region for the release button, a cut was needed on the left side of the tube for the top “hat” portion of release button to fit when in the depressed position shown by arrow D in Figure 29.
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The after the alignment section a flanged surface was designed that necked down to nominal shape, then flanged back out, this is region B in Figure 29. This area between the flanged features is where the grips will reside. The flanged features would locate the grips as well as make the end product look uniform when put together rather than having a big step between the parts. At the lower flanged section a cut away was created in the outside of the tube for the grip to fit into shown by arrow E in Figure 29 and a closer view is shown in Figure 30. This groove locates the grips as well as keeping them from spinning around the body (Samuel & Weir, 1999). After the second flanged feature the body was back to nominal circular shape to the end of the loader which is region C in
Figure 29.
Figure 29 Main body design.
For production the main body of the loader would be made from two part halves during the ejection molding process. The use of sonic welding would join the two halves together. During this process of welding, the spring and the release button cannot be installed so the grips could not be incorporated and would need to be installed after.
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Figure 30 Main body cutout to locate grips.
Grip Design
The grip was designed into two pieces, a left and a right half. These pieces get screwed together via (6) thread cutting screws. The left half design incorporated bosses so the screws would attach and thread into from the right grip. The left grip also had the ribs that guide the release button keeping it in proper orientation. There was a smaller counter bore in the center of the guide ribbing to house the end of the release button spring. This counter bore keeps the spring in position not allowing it to move freely.
Addition ribs were added along the body to keep the handle rigid and prevent flexing.
All these features can be seen in Figure 31. The groove cut in the top side was for the trigger guard to clear. The back side of the left half is completely smooth with no features.
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Figure 31 Left grip inside view.
The right half grip has counter bores in the outside surface so the attaching screw heads are recessed. The counter bore locations match the left grip and use (6) #2 drive 6-
20 x ½” long thread cutting screws which hold the two grips together. The right grip was less complex but still had the same ribs to guide the release button and for overall body rigidity. The views of the right grip can be seen in Figure 32.
Figure 32 Right grip, outside (L) and inside (R) views.
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Pusher Design
The next step was to design the pusher. A pusher was designed to go behind the shells so the main spring was not up against the shells. The pusher was designed as a circular part just smaller than the shell itself with a boss on the back for the spring to fit over and use as a guide, keeping the spring centered on the pusher. The initial problem with this was that when the pusher was in the open end it was no longer be constrained.
When the pusher and the spring went outside of the SSSL top end they could move however they wanted instead of guiding the shells into the shotgun.
To resolve this issue a “t” was added to the bottom of the pusher shown in the
Figure 33. This “t” would follow a similar path opening just below the area where the shells travel in the main body. Once the pusher was in the open area where it was not being restricted inside the tube, the pusher would still follow the path of the SSSL since the “t” would be constraint to the path of the SSSL.
During the modeling, before having a chance to install the last shell into the shotgun magazine, the front bottom of the pusher would hit the shotgun frame. To resolve this issue a notch was added in the front of the pusher for clearance.
The region in the main body for the “t” to travel stops in the same position as the position of the pusher when the last shell has been inserted into the magazine; thus the pusher would not come out the end of the loader.
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Figure 33 Pusher design.
A detailed section view of what the pusher and the release button would look like in a ready position is shown in Figure 34. In this figure the pusher is stopped by the release button with the spring coiled on the back side trying to force the pusher out of the
SSSL. The pusher travels in the middle of the tube guided by the bottom “t” located at the bottom of the main body. The release button was prevented from moving by the ribs on the left grip. The bosses and holes in the left grip are for attaching the right grip.
Once the release button has been depressed the pusher has a clear path to travel and release the inertia built up in the main spring.
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Figure 34 Section view of pusher and release button.
Unlike the TEC loader the pusher behind the shells does not come out the end of the SSSL, it remains inside the product. This means that the pusher cannot be installed into the SSSL during the sonic welding of the main body thus the opening at the bottom of main body was designed. During assembly the pusher would need to be installed inside the main body as well as the main spring. Once the pusher and main spring were inside the main body a cap would need to cover the opening to prevent them from coming out the bottom. A sliding cover plate was created to be able to remove for the installation procedure.
End Cover Plate and End Stopper Design
The end cover plate was designed to be removed to install or replace the pusher if it was ever broken or needed replacing, as well as the main spring. The force of the main spring would be great in the ready to release position so the end cover was designed to be able to withstand this force being applied to it and not come off the main body. A lip was
51 incorporated at the end of the main tube with a hook on the front side. The end cover plate has a “c” shape around the parameter which slides over the lip on the main tube. At the front of the main body where the hook was located, the end cover plate slides into the hook preventing the front edge from tilting downwards, shown in Figure 35. The two interlock preventing the end cover plate from being pushed out the bottom by the main spring.
Figure 35 End cover plate and main tube end design.
The hole in the center of the end cover plate was to locate an end stopper. The end stopper had a nipple on the end that fits into the end cover plate hole, thus keeping the stopper centered. The main body of the stopper would fit inside the end of the coils of the main spring. The purpose of the stopper was to keep the end of the main spring centered inside the tube and prevent unwanted movement towards one side or another.
The concept for the stopper is shown in Figure 36.
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Figure 36 End stopper design.
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5. FABRICATION
During testing multiple things were found that would affect the building, testing and performance of the SSSL. The first was the size of the 3D printer. The accuracy of a
3D printer needed to be taken into consideration because if it was not accurate the parts made on it will come out bigger or smaller than designed. The 3D printer used for testing had a resolution in the Z (vertical) direction of 9.84 e-5” (0.0025mm) and layer heights of
0.0059” (0.15mm), X and Y resolution of 3.937 e-4” (0.01mm). Since 3D printers are relatively small they can only make parts in certain footprints, in this case the build area was 8” wide by 10” deep by 8” tall, which the brand was MakerGear M2. The SSSL was longer than those dimensions so multiple parts were made and had to be glued together.
The problem with gluing parts together to make the entire SSSL was parts had to be aligned and without a fixture alignment could be difficult to maintain concentricity.
There were three critical alignment areas: the top portion left and right sides of the main body, the top portion to the mid-body and the mid-body to the lower body.
The top portion has four parts: left and right main bodies and left and right grips.
The grips would be aligned by the six screws that hold them together, so this was not an issue. The left and right main bodies fit inside the grips so those would need to be aligned with great precision. Other than a little minimal sanding of inside ribs for the grips to fit, no issues came up with aligning the top portion from the 3D printed parts.
The mid-body was a solid piece so the printing of the part was easily designed and made but it needed to mate to the top portion. Each of these two parts had the path for the “t” on the pusher to pass. The two parts, mid-body and top portion, had to be
54 lined up within 0.010” to allow the pusher to pass or else it would get stuck at the joint, which was found from early testing. A simple coupler was created that had the same profile as the outside of each section offset by 0.020”. This coupler would be glued over the top of both mid-body and top portion to align them together. The coupler was taped into position to test before gluing and still had too much play and the pusher would get stuck. A “T” part was made so it fit into the path of the pusher so that it would align everything when gluing and then be removed. The “T” was 0.005” smaller in width than the opening for the pusher to allow for proper alignment. Both the T and the coupler, seen in Figure 37, working in conjunction allowed the part to mate perfectly.
Figure 37 Alignment T and coupler.
The last alignment issue was between the mid-body section and lower body section. The lower body was made from standard PVC tube since the pusher would not be traveling in this section, so no need for the “t” groove. The bottom of the lower body section had a section exactly like the mid-body with the lip for the end cover plate. These were connected by another similar coupler, called an end coupler, and glued. The alignment of the PVC to the end did not need to be exact since just a spring would pass in
55 this region. Between the mid-body section and the lower body a longer end coupler was used to join them. Before they were glued they were taped together using duct tape shown in Figure 38. In Figure 38 Section 1 is the end and bottom, Section 2 is the PVC glued to the bottom, Section 3 is the lower body section (taped with red duct tape to lower body section), Section 4 is the top portion, item 5 is pointing to the grips and item 6 is pointing to the main body coming out of the grip sections.
Figure 38 SSSL fabricated design 1.
This tape worked well for initial prototyping but when trying to load more than two or three shells the tape would lose grip and the lower section would fly off. For actual testing the sections would need to be glued not taped.
Before gluing everything together a thought of what would happen if the spring did not work and another spring needed to be used, but of a different diameter. With all the parts glued together a whole new assembly would need to be 3D printed, which would take a long time since each main body took about 5 hours to print. Using multiple diameters and sizes of springs would have bigger diameters up to 0.875”, these bigger springs would not fit inside a standard 3/4” PVC as shown. Another lower body section
56 needed to be created to test the bigger springs. For a bigger spring a different pusher would also need to be used to correctly fit the spring. Gluing the lower section to the mid-body was not an option. The lower body section needed to be removable to change the pusher for each of the springs tested, as well as change the lower section depending on the size of the spring.
To be able to make the two sections interchangeable some mounting plates were created to fit over the coupler parts at the mid-body to lower section connection point.
The mounting plates were glued over the couplers and each having four holes so bolts could pass and connect the parts together. This allowed for the lower section to be replaced with a different size as well as be able to change the pusher in the mid-body.
The mounting plate designs can be seen in Figure 39. This bolting connection was just for testing purposed until the proper size of spring was selected.
The final design would not have the mounting plates to connect the main body.
The couplers located on the outside of the tube used to connect the PVC tube would also not be included in the final design. The area where the PVC tube was located would have the same body with the “t” groove in it, but one long continuous piece.
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Figure 39 Mounting plates on tested lower and mid body sections.
After all of the parts were fabricated and glued together they were assembled to test. There were two lower sections that would bolt to the upper section depending on the size of spring used. The overall testing SSSL is shown in Figure 40 with the ¾” PVC lower section bolted to the upper assembly.
Figure 40 Overall SSSL design for testing, 3/4" PVC lower shown.
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6. TESTING
Release Button Testing
Testing of the release button found several design flaws. The smaller spring behind the button was acting in the x-direction (towards the right), if viewed from the side, while the main spring was in the z direction (away from the page). Vertically the main spring was higher in the y-direction than the smaller spring so the main spring created a moment on the release button. This moment tilted the release button towards the ejection end of the SSSL along the path of the shells, and up towards the path of the shells relative to the smaller spring.
This extra moment moved the release button higher in the opening of the main body, and also would spin the release button around the smaller spring. These negative effects did not allow the release button to depress far enough to release the shells. The moment that pushed on the release button caused it to hit the wall of the main body tube and not pass through the cutout. The release button needed to be held in position vertically to prevent it from hitting the main body. The original design already had the release button enclosed left, right and on the bottom, so a boss along the top was added.
The new boss was added to the left grip so that it fit in the top left cavity portion of the release button above the spring. As the push button was depressed this extruded boss would prevent the release button from traveling vertically shown in the right image of Figure 41. After the new part was made on the 3D printer it was tested and did prevent the release button from moving vertically and rotating about the spring.
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Figure 41 Redesigned release button in blocking and release positions.
Once the release button was constrained in all the directions but in the motion of the spring one last issue came about, it was the height of the top „hat‟. In theory, and in the model, the top hat covers roughly 15% of a shell, which should have been enough to have the shell catch on it and prevent it from coming out. This overlap was in the ideal perfect situation. In actuality the main springs force was great and the shell pivoted and turned in any direction it could to try and force by release button. While the shell was being pushed by the spring the shell would not remaining in the center of the cavity. The front of the shell would rub against the top and right walls of the main body causing the shell to start to bypass the release button.
Once the shell started to pass by the release button, the main spring applied more force than the smaller release button spring, so the shells pushed the release button out of the way and the shells came out. To resolve this problem the release button was changed
60 so that the curve of the hat went higher up towards the center of the shell. The new design covers almost 25% of the shell in the center position and the difference between the old and new designs are show in Figure 42.
Figure 42 Release button redesign (left), new third design (right).
Pusher Testing
The next problem came from the pusher. The problem with the first “t” design was that the force of the spring was on the center of the pusher. The “t” was constrained only allowing motion along its path but was below where the force was being applied so this created a lever and a moment on the pusher. The moment pitched the bottom down and backwards, while the top went forward and the pusher would stick in the shell path opening and not move. A secondary design of the “t” was created to resolve the tilting of the pusher by elongating the “t” shape. This longer leg of the “t” only allowed the pusher
61 to tilt 0.5 degrees forward, since the trailing edge hits the top of the travel path. This kept the pusher in the correct position and direction for travel which is shown in image B of
Figure 43 (Parmley, 2000).
The pusher observed another flaw in that the secondary “t” design kept breaking during the testing. The fracture would occur right at the bottom of the circle to the top of the “t”. Partly because the material was PLA and the material was weak and cannot handle impact, but also because that was the thinnest section of material. This was resolved by added more material above the “t” shown in image C of Figure 43. The spring still fit over the boss but the added material and increased the strength of the “t” so it would not break as easy.
Figure 43 Pusher design evolution.
During testing another problem occurred that affected the pushers‟ movement.
The pusher was getting stuck and not moving inside the open cavity of the main body with no shells or minimal load on it when the spring was compressed. The pusher would work smoothly sometimes and stick other times. The problem was the interaction
62 between the main spring and the pusher. Springs can be cut so that they have an open end, meaning where the wire stops it is at a rotation and angle, not flat. If the wire were to stand up vertically it would not stand perpendicular to the table because of the angle.
There are three types of common ends for springs shown in Figure 44. Since the open end stop at an angle, depending on where the wire presses against the inside of the pusher, the spring will load the pusher differently (Sclaterm, 2011).
Figure 44 Spring end types.
If the spring end went up against the top of the pusher, more spring force would be on the top of the pusher trying to pivot it downward, thus the pusher gets stuck. The opposite was true for the spring ending on the bottom of the pusher; the spring would try and angle the pusher upwards instead of along the body of the pusher. Having the spring end on the sides worked the best between all scenarios since it would side load the pusher some but not enough to jam. This still allowed the pusher to move in the direction of travel without binding the pusher in the cavity. Images of the different positions of spring wire ends are shown in Figure 45. Inside the body of the pusher at the bottom there was a lip for the notch on the front side, which does not allow the spring to sit flush on the inside of the pusher face; which can be seen in Figure 43 image B or C. With the spring end in the 10 o‟clock position, the spring would touch the inside face and rotate off the face going around clockwise. By the time the spring gets to the lip the spring
63 touches the lip again providing more contact area and more uniform loading. This only works if the spring is rotated into this 10 o‟clock position when assembled.
Figure 45 Examples of different positions of the spring end.
Shell Loading
Loading shells into the SSSL worked but was harder than expected. The shells needed to be pushed down inside the top opening of the SSSL which was not a problem but the depth at which the shells needed to clear the release button was too far down to push with a finger. The first shell on all but the first 3 springs tested was no problem to install by hand, by using the longest finger to push it past the release button. The second shell could be installed on the lighter two springs but not on the heavier springs. The third shell could not be installed on any spring; the force was too great to overcome.
The repeated use of installing shells by hand hurt the fingers, so an installation tool was created to help push the shells past the release button into the loaded position.
Once the shell went past the release button, the release button would go back to ready position because the installation tool was smaller than the inside diameter of the opening
64 around the release button. The install tool worked okay but hard to grip since it was not very long, a longer one could have been designed. The initial thought would be the install tool would fit over the thumb to load the shells. After loading (16) shells the thumb hurt and could not take anymore, so this would not work. The handle from the
Arredondo loader fit onto the install tool nicely, shown in Figure 46. This had a grip to hold onto and worked as a temporary fix but for the final design the release button should be moved closer towards the open end of the SSSL.
Figure 46 Install tool (Left), tool installed on Arredondo handle (Right).
During testing with the install tool it was found that still sometimes the release button would not return to ready position. The last shell would clear the release button and a click would be heard, the sound of the release button touching the main body, but after the install tool was removed and looking into the cavity the release button was not in the normal position, it was roughly 80% of normal position. More investigations and further analysis still needed to be completed to see why this occurrence was happening.
The release button would still hold the shells in place preventing them from being released but not as much surface areas is being used as designed.
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While inserting the shells the release button needed to be depressed to allow the next shell to be inserted. Once the release button was depressed any shells that were already loaded were now free and tried and come out, so the person installing the next shell needed to be ready and start applying force right away. If the installer was not ready for the initial force of the preloaded shells, the force from all of the shells would overcome the installer and shoot out the end. This happened four times when testing.
The shells that come out can and did hit the fingers/hand, since they are in the path of the shells coming out. The shells come out very fast, too quickly to move out of the way and the impact of the shells hitting fingers or the hand hurts and stings for a couple minutes.
Accidental Release Button Triggering Testing
Once all the shells were loaded into the SSSL and the release button was in the ready position multiple trials were taken to see if the release button would engage other than direct engagement. The release button was hit from the side at the base near the grip; parallel to the direction of shell travel, on both the left side and right side of the release button 20 times each. The impacts were conducted by taking a piece of ¼” steel rod, holding it 8” away from the pusher and swinging the steel rod as fast as possible hitting the release button. The impacts in both directions were unsuccessful at releasing the shells. The same process was repeated at the tip of the release button still the same outcome of no shells being released. The button started to crack before the shells were released.
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A new release button was installed then hit at the base and near the tip in the direction perpendicular to the travel of the shells. The pusher was hit swinging the same
¼” steel rod down 20 times and up 20 times for both the base and tip trials. Again none of the 40 test hits proved to release the shells.
The last test for accidental release button triggering was a drop test. The SSSL was held vertically so top of the loader was four feet above the ground. This height was chosen since that‟s the height it would be located if someone was carrying the SSSL on their hip. The loader was released, with a little bias to fall towards the release button side, falling freely to the ground; this was repeated 20 times. During the test the loader would not always land on or hit the release but so the procedure was repeated until the impact of the fall hit the release button 20 times. All tests of falling on the release button never triggered the release of the shells, verifying when fully loaded accidental discharge is very unlikely.
The last item that was investigated before the springs was the stopper. During testing the stopper located in the bottom, which fit up inside the end of the main spring coils, was removed to see if anything changed in the performance of the spring. For the most part the springs remained consistent in the movement and no apparent change was detected when compressed. In the empty state the spring could move a little but not enough to affect the performance. Depending on the spring size, the spring fit well inside the opening since the outside diameter of the spring was 0.875” and the inside diameter opening was 1.040”, which left 0.083” of movement on each side. Using a spring of
0.875” diameter in a 1.040” tube opening the stopper would not be needed. On smaller
67 springs there was room for more movement so the stopper would be needed. When each spring is compressed the force kept enough pressure on the end cover plate to keep the spring position and not move. Thus depending on the final spring chosen the stopper might not be needed in the design and the hole in the end cover plate could be removed.
Spring Testing
A discussed earlier, being able to have the SSSL hold eight shells while maintaining a small overall length was not going to be possible so the decision to change the loader to house four shells was taken. The custom spring from www.springsfast.com was first used to test the SSSL having a loader overall length of 40”. The spring was very difficult to install into the loader. Since the custom spring was 52.21” in the free length it would have to be compressed 40” just to get it behind the pusher at the end of the SSSL. To compress the spring behind the pusher took 15 lbs. of force which was difficult with the assembly already bolted together. Instead the spring was installed into the upper and lower halves and using the bolts at the connection point to join the lower section to the mid-body section which compressed the spring.
Once the custom spring was on the pusher and the loader was put together, the spring needed to be compressed to have the pusher go behind the release button, before any shells could be loaded. Any method that was tried or how much force was applied the spring rate of the custom spring was more than it took to compress the spring by hand. The custom spring was never able to compress enough lock the pusher behind the release button. This custom spring would not work as designed to compress by hand, the
68 force to compress it was too much. This custom spring was spring #2 in the Figure 47.
Looking at Table 2 the force needed to compress the custom spring would have been roughly 99 lbs. for the last shell, thus confirming it was too hard to compress.
More springs were purchased from www.mcmaster.com to test but the longest available lengths were 36” long. This actually worked out better since the SSSL would have to reduce in length, from 40” to 36”, to hold the shorter springs making the loader more manageable. Eight different springs were purchased but only five were tested since two sets of springs were close in size and spring rates and another proved as difficult to install similar to that of the custom spring. Each purchased spring had different specifications for wire size, wire outside diameters and spring constants, which are listed in Table 2.
The custom spring listed was the purchased spring that could not be compressed, thus the N/A in the shell loader column. The Figure 47 shows each spring tested, with each of the spring numbers to the corresponding data in Table 2. During the tests the number of shells being installed into the SSSL was recorded along with the number of shells that were loaded into the shotgun from that particular SSSL loading. Each of the different springs were attempted five times.
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Figure 47 Tested springs inside the SSSL.
The SSSL overall length was cut down to a size of 35.33” long so the loading of the springs behind the pusher was easy to do by hand and each spring had some compression on them in the final state. The distance from the bottom cover to the back side of the pusher is 34.74” so the springs were compress 1.26” initially. Spring #1 was tested next since it had the next highest constant rate which would give a bigger force when compressed in order to load the shells. Spring #1 was very easy to install behind the pusher compared to the custom spring. Getting the pusher down to the release button took some effort but was accomplished. Trying to install the first shell was cumbersome.
Ten different tries to load just the first shell took place but every time unsuccessful.
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Table 2 Testing springs specifications.
To understand why the springs were too hard to load and load the shells Hooke‟s
Law was used, Equation 3. The Load Force was calculated for each spring tested shown in Table 2. Taking the K factor of the spring and multiplying it by the distance of spring compression the load force in the ready position was obtained. The displacement of five shells was 17.675 inches (Usher, 1988).
(3) Equation 3 Hooke‟s Law
The amount of force needed to overcome the spring constant was too high for spring #1. On the tenth attempt the shell slipped off the install too coming out of the
SSSL, which gave the spring a clear path to release and it did. The pusher slammed against the end of the SSSL and broke the pusher right at the base shown in Figure 48.
The broken section from the pusher and where it broke off the pusher are circled. None of the shells were loaded and still the pusher broke, this indicated that the pusher was not strong enough and the force was very high. Any further testing with spring #1 would most likely produce the same result so the next spring was tested.
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Figure 48 Spring #1 with broken pusher.
During all testing of all the springs, with exception to spring #6, if the shells were preloaded into the SSSL and they were released without being held up to a shotgun, the pusher would break at impact at the end of the SSSL. The force of the springs were high behind the pusher because there was no counter action of a shotgun magazine spring pushing back on the shells from being loaded, the full force of the main spring would impacted on the pusher to the end of the loader. The material properties of PLA, which was used to fabricate the pusher, shows that the impact resistance is very low (0.88 ft- lbs/in) compared to a polyurethane material (800 ft-lbs/in), which would be used for the final product. The final product should not have this problem since the impact resistance it so high (Stronge, 2004).
The spring #3 was tested next since it had the same outside diameter as the #1 spring, so the lower section of the SSSL would remain the same. Spring #3 was almost four times lighter than the previous spring tested so the ability to install shells behind the release button took place. The pusher was able to go behind the release button with little effort and no use of the install tool. Shells were loaded into the SSSL, which on the first
72 attempt (4) shells were installed. To test and make sure shells would come out the loader, the release button depressed without the loader being held up against the shotgun. All the shells rapidly left the SSSL without any resistance or problems.
The SSSL was loaded again with (4) shells using spring #3 and held to the shotgun for insertion. The first two attempts only (2) shells were loaded into the shotgun, but the results looked promising and the loader was working. While loading shells into the SSSL on attempts 3 through 5, (5) shells were able to fit into the loader in the ready position. On the last three attempts (3) shells were loaded into the shotgun, while the 4th shell was partially loaded and the 5th shell was at the end of the SSSL.
The lower section of the loader was removed which used the 1” PVC and the ¾”
PVC lower section was installed for the smaller diameter springs. The spring #4 was then tested to compare the results in the ¾” PVC. Spring #4 could easily install (4) shells into the SSSL each time tested. On the last two attempts (5) shells were installed into the
SSSL. On all attempts with spring #4, all but one shell was inserted into the shotgun. The best result was (5) preloaded and (4) into the shotgun. This was a great improvement over the other tested springs. The rate constant on spring #4 was a little higher than spring #3 which gave more force to load another shell into the shotgun.
Spring #5 could easily load (2) shells into the loader by hand. Five attempts were taken and (5) shells preloaded into the SSSL each time very easily, and every time only
(2) loaded into the shotgun. The 3rd shell was partially loaded, sticking out the loading port and the 4th and 5th at the end of the SSSL. Spring #5 had the lowest rate constant, by
73 putting in more shells it would compress the spring more creating more force, hoping it would install more shells than the spring #4 but did not work as expected.
The smallest spring was tested last, spring #6. This spring had a rate constant similar to spring #3 but the outside diameter was much smaller. Surprisingly (6) shells were able to be loaded into the SSSL ready to be released. On all five attempts only (1) shell was loaded into the shotgun. This was unexpected since the same spring rate loaded
(3) shells using spring #3, but the diameter of the spring was much smaller which hurt the loading procedure since the spring could move in the tube. All of the data for the tests of the various springs can be seen in Table 3.
Table 3 Spring test loading data, original training shells.
Preloading the SSSL three more times and releasing the shells using spring #6, away from the shotgun, the spring was heard hitting the walls of the PVC tube. This was happening because as the spring was being compressed it formed a wave motion inside the PVC tube, it did not compress linearly. If a section view was observed the compressed spring would look like a snake or sine wave. The spring was doing this because of the size of the PVC tube. The inside diameter of the PVC is 0.75” and the outside diameter of the spring is 0.562”. The extra distance between the two allowed the
74 spring to flex as needed to be compressed more. When the spring was released the force was dissipated by extending the spring back to straight position as well as forward, instead of all the force going in a linear motion forward. The only way to eliminate this from happening was to have the springs outside diameter just smaller than the tubes inside diameter. Having this could be done on the lower half but once the spring was on the upper half where the shells travel it would impossible to have a close fit since the shells are 0.878” in diameter. Thus spring #6 would not be suitable for this application and was eliminated from the choices to be used.
After all of the tests were taken the shells were gathered and inspected. The shells‟ outside edge of plastic was starting to flare out. From the repeated motion of hard impacts to the front of the plastic of the shell they were becoming deformed. Any time the shells did not enter the magazine correctly they would hit something like the frame or another shell it caused the end to flare out. Both new (red on the left) and deformed shell
(green on the right) can be seen in Figure 49. The deformed shell would still fit into the magazine chamber by hand but all clearance was eliminated. This was problematic because the loader would not be able to work correctly if the tolerances of shells to shotgun were not as designed. So these deformed shells could have skewed the testing results so it was decided to run the tests again.
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Figure 49 New and deformed shotgun shells.
New shells were used to retest each of the springs to see if having the proper clearances would change the outcome of the results. The first and second springs were not tested because they were not able to compress enough to load the shells. The fifth spring had the exact same results as the original training shells. The sixth spring loaded the same amount into the SSSL and loaded one more into the shotgun but only (2) into the magazine was not desired. The third spring also was able to constantly load one more shell into the shotgun over the original shells, but never had all (5) load into the shotgun.
All of the numbers for second testing using new shells are shown in Table 4 for each spring.
The best spring was #4 on retesting with new training shells. This spring loaded the same amount into the SSSL but every time tested, assuming a good grip on shotgun and loader, all (5) shells went easily into the shotgun. This was the best situation and purpose of the device; having all shells that were loaded into the SSSL transferred into the shotgun. Two different times while retesting the grip on the SSSL was not strong
76 enough to keep the loader up against the shotgun frame, four shells would load but not the last shell.
Table 4 Spring test loading data, using new shells.
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7. ANALYSIS OF THE DATA
The spring #4 was the best spring from the testing data and it was calculated at having 22.59 lbs. of force, from Table 2, at the ready position to transfer the shells to the shotgun. Looking at the measured force for the 5th shell using the force sensor the average was 23.9 lbs. The difference between the measured and actual spring was 1.49 lbs. having an error of only 6.2%, which was good and confirms the measured and actual spring does what was measured and intended. Spring #3 also was able to hold (5) shells into the loader but never was able to load the 5th shell into the shotgun. Looking at the amount of force required of 23.9 lbs. and the amount of force the spring #3 had preset of
17.29 lbs. explained why the 5th shell never was loaded; there was not enough force to load the last shell.
Once all the shells were loaded into the SSSL and they are ready to be inserted into the shotgun it was noticed the force to hold the SSSL up to the frame could be difficult for some people if unsupported or held by one hand. When the release button was depressed the main spring applied a force against the shells causing them to go out of the SSSL. By Newtown‟s Third Law, for every action there is an equal and opposition reaction, now comes into consideration. The force that was applied to the shells was also being applied to the body of the SSSL at the bottom. If there was no one holding the
SSSL and the release button was pressed the whole body of the SSSL would shoot out backwards away from a shotgun. During multiple tests while holding the SSSL the whole body of the loader moved inside the hand if a tight grip was not applied. This movement forces the SSSL away from the frame and does not allow for proper feeding of
78 the shells into the shotgun. This reaction took place more on the higher rated springs, numbers 3 and 4. The smaller rated spring had the same movement but the reaction downwards from the SSSL was not enough to overcome the hand grip strength by the loader so the SSSL remained solid against the shotgun frame.
After the final design spring was chosen, spring #4, more trials were conducted to see if the spring would consistently load the shells or if the spring would start to lose resistance force and not be able to load them all after time. The test was conducted 53 times, which was not enough to get an accurate evaluation but a good start. Only 53 trials were performed because of two conditions, the first was because the shells were becoming deformed after 5 loads so new shells had to be used, the amount of shells on hand to test were limited so not having enough new shells to run more tests limited the testing. The second problem that reduced the trial numbers was that the pusher sometimes was stuck on the loading ramp shown in Figure 50.
Of the 53 trials 9 times the pusher became stuck in between the loading ramp and the end of loading chamber. In order to release the pusher from this position the SSSL would be angled towards the front of the shotgun, and the loading ramp would have to be pushed up into the frame allowing the pusher to pass in between. During testing of spring #4, roughly 17% of the time, the pusher would stick in the shotgun during loading.
With the pusher becoming stuck during loading was not having a repeatable and consistent product. Another design change would need to take place on the pusher to prevent this from happening.
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Figure 50 Pusher jammed in loading port on loading ramp.
The last data analyzed was the rating of the spring compared to the force required to load a shell. During the measuring of the force it took to load the shells for five shells it took roughly 24 lbs. of force. The state at which this was measured was four shells were preloaded and in a static condition. The shotgun magazine spring was compressed and was pushing back on the end of the loaded shells. The spring #4 that was chosen had about 23 lbs. of stored energy in the „ready‟ state of the loader.
Previously it was thought that when the SSSL spring was at the end of the travel it would need the force measured by the fifth shell. In actually, the force of the main spring, was compressed, had that much force greater than the measured fifth shell, the loader worked.
Imagine a perfect world with no loss due to friction where a spring was in a tube compressed with five shells, and that same tube had another spring of same rating on the other end. Once the compressed spring was released all the energy would be transferred
80 to the shells which would get transferred to the other spring, compressing it the same amount as the first spring. These two springs would go back and forth treating the shells like a tennis ball on a tennis court. The same principle applied here in which the highest amount of stored energy was transferred to the magazine spring, by the first shell, compressing the magazine spring enough to load all five shells. By the time the last shell was loaded into the magazine, the magazine spring in the shotgun was still compressed and had not started its return to full length. The force needed to load the shells was not needed at the end of the SSSL travel but only in the ready position.
After all the testing was completed and spring #4 was chosen the model was updated to reflect the overall length and design of the SSSL shown in Figure 51. The middle had the bolted together section removed since it will be injection molded as one piece.
Figure 51 Final design and overall views of SSSL.
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8. CONCLUSION
The original plan was to make the SSSL hold eight shotgun shells, making it the first shotgun speed loader to do so in a single tube. Going through the design and calculating how large the spring would be to force the shells into a shotgun was feasible but the length of the loader would be longer than desired. This length of the compressed spring plus the shells puts the SSSL at well over a length of 4 feet long, which would be considered by most too long to hold on a person‟s side and still be able to maneuver. The
SSSL was reduced to (5) shells to obtain a somewhat manageable length of the loader.
The amount of shells preloaded was comparable to other loaders currently on the market so the SSSL would provide competition in sales for them.
With the SSSL holding (5) shells the overall length was at 35.33” long which was still very awkward to hold or have attached to something on a person‟s hip. The current market has a four shell speed loader, so a future option would be to reduce the SSSL to only (4) shells. By eliminating one shell, the length could reduce by 2.36” as well as the spring length reducing. The spring force would not need to be as high since less shells are being loaded into the magazine, thus the spring could be cut to a smaller length, or compressed more. This new length would need to be calculated and determined how much length would actually be saved. If only 4” total was removed, having the extra shell might be worth the current length. If the loader was reduced by 10” then having only four shells would be a viable option since the length would be greatly reduced.
A couple changes for the speed loader need to happen to enhance the features, reliability, usability and efficiency. The first improvement would be to move the release
82 button further up the SSSL towards the opening where the shells come out. This would do three things: reduce how far you have to push the shells into the SSSL, reduce the overall length and remove the need for an install tool. The length would reduce by the difference in the current release button position to the new position.
The second improvement would be to change the grips on the left and right sides of the main tube to better fit the hand and provide a better feel. Currently someone can hold them and work but an ergonomic shape would make it more appealing such as finger indentions. This would make the SSSL easier to grab from any position, and would make the unit easier to hold on to when pushing the release button. Adding a texture to the grips would help with the hand contact grip; this texture would be put into the mold so the end product would come out of the mold with a finished texture.
The release bottom still needs to be investigated why it was not returning back to normal position after the shells were installed. The install tool clears the release button while holding the force of the main spring off the release button, so no real force should be on it. When the install tool was removed, with shells loaded, the release button was not in normal returned position every time. One thought was the tool actually does not clear the release button, thus not letting it come out to normal position before the shells touch the button. The spring and shells were remove and the assembly taken apart so the internals could be seen down the end looking towards the release button. The install tool was inserted and it passed over the release button without any engagement, so that was not the cause. Another idea was that the opening for the release button to pass through was too tight; and the release button stuck on the sides of the cut out. Taking the
83 assembly apart the sides of the release button did not show any wear marks so this idea was eliminated. Another thought was that the smaller spring behind the release button was not strong enough. The first one or two shells loaded the smaller spring could handle but when the larger force starts to apply to it perpendicularly, the smaller spring starts to compress and cannot fully extend. Ultimately more investigations need to take place to solve this issue.
Any misalignment or not being ready when loading a shell, when shells are already preloaded, can potentially cause injury to the loader. The force and speed at which the shells come out of the SSSL are very high. If a hand or arm was in the path of the shells being released someone could be hurt. This device is not a toy and should never be used as one. An improvement needs to be made to have a safety lock or something preventing someone from accidental discharge during the loading process.
This would also make the loading process easier to prevent miss-loading or releasing the shells while loading. Once the shells are loaded, the release button takes direct force in- line with the release button to eject the shells. Bumping or hitting the release button by accident will not discharge the shells.
The issue of alignment of the spring wire end to the pusher would need to be resolved so that when assembled, no matter the position of the spring wire end was located, the pusher would move smoothly. This would have to be done by eliminating the single point of contact between the wire and the pusher. The spring would be designed to have a closed end. The pusher would also have an entirely flat surface so that in any position the pusher and spring when put together both would mate around the entire
84 diameter face. This would provide a uniform load on the entire face in the direction of motion eliminating any changes of the pusher being jammed. A problem with this is method is the cost of a closed end spring for production is more than an open end and the spring can still move around on the face of the pusher so it is not concentric.
An alternative method to having a closed end of the spring would be have the middle of the pusher, which goes inside the spring, have a bigger diameter than the inner diameter of the spring. This would start off smaller and get bigger in a tapered fashion.
The spring would fit over the cone body and get tighter around it since the cone gets bigger as it goes down to the base of the pusher. The spring would always be centered on the pusher and the force would always be pushing on the center of the pusher.
While the pusher was being modified to accommodate the spring change, it would also be changed to prevent it from becoming stuck in between the loading ramp.
Currently with the pusher in the end position, pushing the last shell into the magazine there is enough clearance between it and the loading ramp, so the loading ramp falls onto the pusher and gets wedged. To correct this, the top of the pusher would have an extension coming out the top back ¼” to fill this gap. This extension would be just like the curve shape above the “t”, the final design is shown in Figure 52. With the new change to the pusher, in the end position, when the loading ramp moves down the ramp will rest on top of the flange of the pusher instead of in between it.
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Figure 52 New design of pusher to try on next iteration.
The SSSL is to be injection molded. Since the overall length is very long, tooling for a mold might be an issue. The main tube will be molded into two halves and sonic welded together. Discussions with an injection molding company will determine if a single mold can be used or if another route will need to be taken. The SSSL main body can also be broken into four pieces and all four sonic welded if necessary thus reducing the size of the molds. The more pieces the more chance of misalignment during the sonic welding. The pusher, the release button, end cap, left grip and right grip all will be injection molded as a single part and the size of those are not an issue.
The last and most important item to address is user testing. After all of the design changes noted in this paper have been having average users test and use the SSSL for feedback is critical. Having experienced and novice shotgun shooters use the SSSL
86 would provide valuable feedback in the design that might have been overlooked. The suggestions and feedback from actual users would help make the product better, more user friendly and help find any flaws in the design.
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Appendix A Individual Part drawings
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Appendix B Interlink Electronics FSR 402 Specifications
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Appendix C Arduino Specifications
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Appendix D Arduino Programming Code w/ 5 lbs. & 10 lbs. Verification
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5 lbs Weight Verification
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10 lbs Weight Verification
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Appendix E Shotgun 12 GA. Shell Measurements
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