4/12/2015 Bullet Design and Feeding Reliability
This page was first published online 7162010
Bullet Design And Feeding Reliability In Semi Automatic Pistols
by
http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 1/20 4/12/2015 Bullet Design and Feeding Reliability Brad Miller, Ph.D.
A modified (and newer) version of this article has been published by Guns and Ammo here:
Miller, B. Keep that gun running; An indepth look at bullet nose design and feeding reliability in semiauto pistols. Guns and Ammo 2013 Annual, 171176.
The original version of this article is being published here.
Bullet design features can contribute significantly to reliable feeding in semiautomatic pistols. Not all guns are particular about what you feed them. They run reliably with everything. Other guns are picky eaters. The picky eaters are frustrating, but can highlight what design features contribute to reliable feeding, and small changes in bullet design can make big differences in reliability.
It is sometimes difficult to dissociate gun issues from bullet issues. In many instances it does not matter which one you blame for the problem: the bullet or the gun. It boils down to compatibility: does that particular gun feed that particular bullet reliably? If it doesn’t, something has to change. Sometimes the bullet is the guilty party.
Finding a reliable feeding bullet is sometimes simple, but sometimes a complex and multifactorial problem. What should we look for when selecting a reliable bullet? The principal features of bullet design that influence reliability are their construction and nose design. The bullet’s composition and construction can influence its relative integrity and lubricity when interacting with surfaces during the feeding process. Nose design can significantly affect how the bullet interacts with the feed ramp, and cartridge overall length, another critical factor in feeding reliability that is discussed below.
This article highlights important features of bullet construction and detailed features of nose shape that are often overlooked but can make the difference between a smooth running pistol and a jamomatic. Real world examples are given for illustration.
Let’s begin with the basics, bullet construction.
Bullet Construction
There are several ways to manufacture bullets. The methods and materials define relative hardness, an important variable in feeding reliability. Handgun bullets are swaged, cast, plated, jacketed, total copper and frangible (Figure 1). Lead is the common element, except total copper and frangible bullets which are lead free.
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Pure lead is soft and tends to deposit lead in the bore from friction (leading). Pure lead has a high friction coefficient and does not slide along or bounce off surfaces well, and this can produce feeding problems in semiautomatic pistols. Consequently, lead alloys that include tin and/or antimony are often used when lead is in contact with the barrel bore and feed ramp.
Swaged bullets are formed by pressing a soft lead alloy into a mold at room temperature. Their hardness can be regulated by changing the alloy, but it must be relatively soft to remain malleable enough to fill the mold completely and form the proper shape. Swaged bullets for semiautomatic cartridges are then generally lubricated with a dry lube, often waxy or something such as molybdenum disulfide (MoS2; a.k.a. moly). The lubricant enhances feeding reliability and reduces leading. Because swaged bullets are relatively soft, the general rule of thumb is that they should not be driven over around 1000 feet per second (fps) to reduce leading.
Cast bullets are made by pouring molten lead into a mold and allowing it to cool to a solid. The casting alloy can be much harder than the alloy used in swaged bullets because it fills the mold as a liquid. Cast bullets generally have a groove (or several) around the body for lubricant, often made from a waxy material. Some manufacturers coat the entire bullet with moly or other material, even copper plating. Since cast bullets are relatively hard, they can be driven to 1500 fps or more if made of the proper alloy.
Plated bullets usually start out as swaged bullets. Then a thin coating of copper is applied electrochemically a molecule at a time (think powdered donut) to form a layer adhered to the lead core. The copper layer’s thickness can be controlled and varies depending on the manufacturer and their intended use. The plating is very thin compared to the usual copper jacket of jacketed bullets (Figure 2), so the bullet’s hardness is determined by the lead alloy core.
Berry's, Rainier and Speer plated bullets are the more common brands in the U.S. Some premium hunting and selfdefense bullets are plated, for example, Speer’s vaunted Gold Dot bullets.
Copper plating fully encapsulates the lead core resulting in a seamless covering of copper (Figure 3). These bullets are often referred to as having a Total Metal Jacket (TMJ). This greatly reduces airborne lead molecules because there is no exposed lead at the base that can be melted by hot gases from the burning gunpowder.
Some plated bullet manufacturers (Berry’s, Rainier) suggest that their bullets not be driven faster than around 12001250 fps. These velocities do not always make Major power factor when used in 38 Super caliber open class competition guns, so these shooters often turn to jacketed bullets. However, Speer does not indicate a speed limit with their plated bullets (Reloading Manual #14). Berry's recently added a line of http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 3/20 4/12/2015 Bullet Design and Feeding Reliability bullets with a thicker plating that allows them to be pushed to 1450 fps.
Jacketed bullets are composed of a lead core inside a sheet of copper, often gilding metal (95% copper 5% zinc) or other soft metal. Montana Gold bullets incorporate a brass jacket, as does Remington’s Golden Saber. Brass is a copper alloy with a higher percentage of zinc, around 10%. Brass jackets can be harder than gilding metal jackets, but this is somewhat unpredictable because the alloys can be work hardened (Norm Bjelland, Montana Gold Bullets). For comparison, cartridge brass is generally a 70/30 copper/zinc composition (www.brass.org).
Jacketed bullets start out as separate components (lead core, copper alloy jacket) that are later combined into the final shape. The hard external jacket starts out as a plug or sheet that is pressed into a cup shape, then filled with the soft lead core, and shaped to its final form. This process leaves one end of the bullet with exposed lead, either the front (soft point, hollow point) or the rear (full metal jacket (FMJ)). Hornady and Montana Gold cover the exposed base of some of their FMJ bullets with an additional copper cap, and rename them Full Metal Jacket Encapsulated (Figure 3) and Complete Metal Jacket, respectively. This effectively reduces airborne lead. Jacketed bullets can be driven to over 4000 fps, and therefore have no velocity limits in handgun cartridges. http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 4/20 4/12/2015 Bullet Design and Feeding Reliability Solid copper bullets are made from pure copper or copper alloy and consequently are inherently hard. They are formed principally through swaging. Barnes Bullets machines some of their crimp grooves1. They have no velocity limits in handguns.
Frangible bullets are formed from powdered metal or metals such as copper, tin, tungsten, zinc, bismuth, iron, and steel and sometimes include a polymer compound. The material is compressed into the desired shape. Sinterfire’s frangible bullets are made from copper and tin and incorporate a proprietary lubricant. Their composite bullets are “sintered” (baked) to enhance integrity and performance (www.sinterfire.com).
Frangible bullets are hard and brittle – by design. They are intended to disintegrate into powder (its original form) on impact when encountering something harder than itself, reducing the ricochet hazard. (Frangible bullets should not be confused with prefragmented bullets like the Glaser Safety Slug.) This design is ideal for steel targets since they produce smaller fragments that make them safer to use than lead based bullets. Frangible bullets have no velocity limits in handgun cartridges. Bullet Shape: The Nose Knows
The bullet nose interacts with the feed ramp and chamber entrance during feeding, and its shape can be critical for reliability. Nose design also affects cartridge overall length which determines when it hits the feed ramp and the cartridge’s angle when it is released by the magazine’s feed lips and when it encounters the chamber. Thus, bullet nose design affects feed timing.
Some nose shapes are inherently more reliable feeders than others. Generally, round nose bullets feed more reliably than flat nose bullets. Some flat nose bullets feed more reliably than others because of small but significant differences in their design. These features are discussed below.
Nose Shape
The principal distinction in bullet geometry is the shape of their nose. Pistol bullet nose shapes fall into two categories, round nose and flat nose. Round nose bullets are distinguished by the shape of the ogive (the rounded curvature of the nose). They vary from being somewhat pointy to downright blunt. Flat nose bullets for semiautomatic pistols can be broken down into shape subcategories. The common shapes are shown in Figure 4A. The shape of the shoulder and sides of the nose vary in design. (The terms flat nose and flat point are used interchangeably.)
Round Nose (RN) bullets have a slight change of angle at the shoulder and curved sides of the nose leading to a round point. This is a common design for semiautomatic pistol bullets, with the exception being .40/10mm caliber bullets that are designed principally with a flat nose.
Round Nose Flat Point (RNFP) designs have a gradual change of angle at the shoulder and curved nose sides leading to a flat point. Many hollow point bullets follow this design.
Truncated Cone (TC) bullets have an abrupt change of angle that forms the shoulder and straight, tapered sides leading to a flat point. This design is common for .40/10mm caliber bullets.
SemiWadcutter (SWC) bullets are easily identified because they have a sharp, often 90 degree, abrupt edge at the shoulder and (usually) straight, tapered sides leading to a flat point. Round nose versions can also be found. SWC bullets have a wide shoulder “ledge” that makes a clean, caliberwide hole in paper targets.
Rebated (or Recessed) Nose (ReN) bullets have a short, abrupt shoulder, similar to the semiwadcutter design, but not nearly as wide. The nose side is sometimes parallel with the driving band for some distance. The nose point can be round or flat. This design usually does not produce a clean, caliber wide hole in paper targets like semiwadcutter bullets. http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 5/20 4/12/2015 Bullet Design and Feeding Reliability
Bullet Shoulder Design
The shoulder is the transition between the bearing surface (a.k.a. driving band, shank) and the nose. The shoulder can be an abrupt edge typical of semiwadcutter bullets or a gradual transition from the bearing surface to an arc on round nose (and RNFP) bullet designs. Examples are shown in Figure 4B. The shoulder design is illustrated by the blue line. The shape of the shoulder determines how the bullet engages the barrel riflings.
Flat Point Radius
The flat point radius is the transition from the nose taper or curve to the flat point. Some bullets have a short, sharp radius (almost nonexistent), while others have a wide, rounded radius. Examples of the flat point radius are shown in Figure 4C. The red arc denotes the radius design. The shape and width of this radius can be a critical factor for reliable feeding because a wider, rounded radius can give a flat nose bullet an almost roundnoselike profile where it interacts with the feed ramp and chamber entrance. A short radius can act like an edge that will catch on other edges.
Nose Length/Width
Bullet nose length can influence cartridge overall length, which affects feeding reliability. Nose length varies considerably by design and manufacturer. Examples are shown in Figure 5. The bullet’s nose length is http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 6/20 4/12/2015 Bullet Design and Feeding Reliability illustrated by the vertical black line to the right of the nose. It indicates the length from the shoulder to the tip. The red arc indicates the flat point radius, where appropriate. A given manufacturer might, or might not, maintain the same structural features of bullet shape in their product line, even within the same caliber. For example, Hornady’s 124 grain FMJ FP bullet has a relatively wide and rounded flat point radius while their 125 grain HAP has a short one (Figure 5).
Flat nose width also varies considerably and can be an important factor in feeding reliability because it determines where and when, it hits the feed ramp. Wider flat noses hit lower on the feed ramp and sooner than narrower designs. More information on how nose length/width can affect feeding reliability is given in the Overall Length section of this article.
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Bullet Design and Feeding Reliability
There are many factors that can cause feeding problems. If you stay in this sport for very long you’ll likely see so many different types of feeding malfunctions that you can’t count them on all of your fingers and toes combined. Keeping on top of mechanical issues that affect reliability (magazines, extractors, springs, rough surfaces, brass, tolerances, lubrication, crud, etc.) is headache enough. The following discussion illustrates how bullet features can influence reliable feeding.
Round and Hard
The two bullet characteristics that enhance feeding reliability the most are roundness and hardness. Rounded features negotiate the feed ramp and chamber entrance best, and hardness means that the bullet will slide/bounce along happily with minimal friction. Other factors come into play, such as overall length, but generally, the traditional round nose full metal jacket bullet is the gold standard for reliable feeding. http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 8/20 4/12/2015 Bullet Design and Feeding Reliability Roundness by itself does not guarantee reliable feeding. Soft round nose bullets (swaged, plated) sometimes present feeding problems. My .45s (single stack and double stack 1911s) don’t like plated bullets (of any shape). I have tried many variations of plated bullets over the years, both factory loads and handloads. I expected the round nose designs to feed reliably because of their shape and slippery copper plating. However, some of the plated bullets would stop dead when they hit the feed ramp, or when they just begin to enter the chamber while the cartridge is still at an angle. Switching back and forth between plated and FMJ bullets with the same nose shape (and overall length, etc.) reinforced the notion that the plated bullets were the problem. The question is why? This question becomes more perplexing when soft bullets that won’t feed have the identical shape as hard bullets that will feed. The rounds in Figure 6A illustrate which bullets with identical profiles will/won’t feed in the author’s .45s. (It’s important to point out that many pistols feed plated bullets just fine. It’s an individual gun issue.)
While looking closer at this issue I noted a significant difference in how hard and soft bullets respond to the surfaces they contact during feeding. When soft bullets (swaged, plated) hit the feed ramp, they deform significantly more than hard bullets (cast, jacketed, frangible). Figure 6B shows differences in the size of the deformation on the bullet nose between a soft swaged bullet and a hard cast bullet after hitting the feed ramp (contrast enhanced photograph). The dent on the swaged bullet is 2.9 times larger. On the opposite side of the bullet nose is a contact dent where it hits the top inside of the chamber. These contact areas are also clearly larger on soft bullets than hard bullets. The larger dent increases the surface area in contact with the feed ramp and chamber, which likely increases friction, and perhaps the copper plating is not as slippery as presumed on soft bullets. Plated bullets sometimes suffer from greater setback when they hit the feed ramp than jacketed bullets, which could reduce momentum, further slowing them down. While it’s not obvious why these bullets won’t feed 100% reliably in the author’s pistols, they repeatedly fail to do so.
On the other hand, a soft RN does not necessarily predict unreliable feeding. My same .45s that don’t like the plated RN bullets feed the Hornady 230 grain RN swaged lead bullets (Figure 6A) just fine – though I’ve not tried thousands of them, only hundreds. Still, the swaged Hornadys run smooth, with no signs of sluggish slide movement despite showing an enlarged flattened region after hitting the feed ramp (Figure 6B). Their dry, waxy lube works well with my pistols.
Being hard does not guarantee reliable feeding, either. Nose shape and cartridge overall length can be the deciding factor, as various examples that follow will illustrate.
Nosedives
If nosedives are an issue in your platform, the bullet nose design can significantly influence reliability. A wide flat nose means the bullet will hit lower on the feed ramp than a round nose bullet. In some cases the edge of the flat nose bullet can hit below the gun’s designed feed ramp. Figure 7 shows a nosediving 45 ACP round with a flat nosed Barnes hollow point bullet whose lower edge will hit well below the cutout for the http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 9/20 4/12/2015 Bullet Design and Feeding Reliability feed ramp. Nosedive related feeding problems can sometimes be resolved by using round nose bullets, and hard ones often fare better than soft ones.
(Figure 7. Front view from a single stack 1911 frame cut for a Clark/Para Ordnance type ramped barrel. The cartridge is the top round in a fully loaded 8 round magazine and is positioned at its full nosedive angle.)
Nose Length
Short nose bullets have to be seated deeper in order to fit in the chamber without engaging the riflings. This results in a short cartridge overall length, which some guns might be sensitive to. Cartridge overall length affects timing since it determines the location of the slide when the cartridge first engages the feed ramp and the cartridge’s angle when the case is released by the magazine’s feed lips. Specific examples of how overall length affects feeding reliability are given below in the Overall Length section.
Small Change, Big Difference
In a perfect world we could use round nose bullets and be perfectly happy. But sometimes flat nose bullets are preferable. Most handgun bullets designed for selfdefense and hunting are flat nosed hollow point, soft point or just plain flat nosed. And flat nosed bullets are the norm for 40 S&W and 10mm. Accuracy can also differ between round nose and flat nose designs, the nod usually going to the latter.
Some pistols can be reluctant to feed flat nose bullet designs. But the details matter, and minor design differences can make a big difference in feeding reliability. Here is a realworld example. My Colt .38 Super shoots flat nosed bullets more accurately than round nose bullets, so I select them for competition. However, some flat nose bullets feed well in my gun, while others don’t.
The bullets that don’t feed failed because of the feed ramp design. Colt uses the conventional twopiece feed ramp – both the frame and the lower face of the chamber entrance form the feed ramp (i.e. a nonramped barrel). This gun’s barrel feed ramp is narrow. Widening the barrel’s feed ramp (throating) might solve the problem, but selecting a bullet with a minor change in the flat nose radius was all that was needed.
http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 10/20 4/12/2015 Bullet Design and Feeding Reliability One bullet that would not feed reliably in this gun was the Zero 147 grain JHP. It has a short, sharp flat nose radius. The edge of its nose would catch on the bottom edge of the barrel’s feed ramp (noted by the arrow in Figure 8). Other bullet designs like it jammed in the same fashion. But some flat nose bullets feed perfectly. One is the Remington 147 grain FMJ bullet. It has a wide and rounded flat nose radius that allows it to negotiate the feed ramp and chamber entrance as reliably as a round nose bullet. This illustrates one example of how bullet design can overcome gun design limitations.
Careful Handloading Required
Frangible bullets require more precise tolerances during handloading. The critical step is crimping. Depending on the bullet contour, no crimp or only a very light taper crimp is recommended. Sinterfire’s frangible bullets, for example, have a tapered nose (a variation of a rebated nose) and are designed to be lightly taper crimped at a “predetermined depth” (www.sinterfire.com).
If too much crimp is applied and the case mouth pinches the bullet, the bullet can crack, and this can result in bullet nose detachment. If you’re lucky, you’ll see the cracked nose during your handloading process and can start over with a fresh bullet. If you’re not so lucky, the cracked bullet can cause a spectacular feeding malfunction if the nose detaches during feeding, or can show up on your target as two hits after a single shot. Figure 9 shows examples of these pitfalls. All of these problems can be avoided with the proper crimp. Their hard nature enhances feeding. Nose Shape and Cartridge Overall Length
The overall length of the cartridge is a very important detail. Manufacturers and handloaders must pay close http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 11/20 4/12/2015 Bullet Design and Feeding Reliability attention to overall length to produce reliable, safe ammunition. Bullet nose shape is critical in determining overall length. When loading any pistol cartridge, the golden rule is: not too long, not too short. Generally speaking, the length of the loaded round should be as long as possible to enhance feeding reliability, but not so long that it jams in the magazine or in the chamber. And the bullet should not be seated so deep that it hampers reliable feeding or pushes pressure too high.
Fit in the Magazine: Nose Shape
Bullet nose design can determine the maximum overall length of the loaded cartridge that will fit in the magazine. While many magazines will accept a round nose bullet loaded to the SAAMI maximum overall length, they might jam with a flat nose bullet loaded to the same length. Why? Because bullet nose design affects the loaded cartridge’s diagonal length. This matters because cartridges lie in the magazine at an angle. If the diagonal length is too long, the cartridge will get stuck. The upper portion of Figure 10 shows two cartridges of the same overall length but with different bullet designs as they would lie in a magazine. The cartridge with the flat nose bullet won’t fit in the same space as the cartridge with the round nose bullet.
Another feature of pistol magazines is their round front profile, which is illustrated in the lower portion of Figure 10. Both single and double stack magazines have a round front profile, though many double stack magazines also have a central flat portion. This rounded contour can also limit the cartridge’s overall length. Flat nose bullets must be seated deeper in order to fit.
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Figure 11 illustrates the diagonal length of four semiautomatic pistol cartridges with round nose and flat nose bullets (except 40 S&W, see below) when the overall length is at the maximum SAAMI length (vertical black line). The diagonal length (diagonal blue line) of flat nose bullets is significantly longer than that of round nose bullets. The 9mm Luger example shows a diagonal measurement difference of 0.019 inches between round nose and flat nose bullets when seated to the same length.
(Bullets used for the measurements: 9mm Luger; Round Nose, Zero 124 FMJ. Flat nose, Sierra 125 JHP. 38 Super; Round Nose, Remington 130 FMJ. Flat Nose, Hornady 147 HP/XTP. 40 S&W; Narrow Nose, Montana Gold 155 JHP. Wide Nose, Speer Gold Dot 155 HP. 45 ACP; Round Nose, Hornady 230 FMJ. Flat Nose, Sierra 230 JHP. The actual diagonal length varies with the specific bullet.)
Another point illustrated in Figure 11 is that wider flat noses have a longer diagonal length as well. The 40 S&W cartridge is shown with two flat nose bullets (narrow and wide) because round nose bullets in this caliber are not common. The difference in diagonal length between the narrow and wide flat nose bullets is 0.011 inches. Thus, the width of the bullet’s tip is important with respect to cartridge diagonal length. This distinction also applies to “pointy” versus “blunt” round nose bullets. Blunt round nose bullets have a longer diagonal length than pointy round nose bullets when they are loaded to the same overall length, though the difference is small.
Fit in the Chamber: Nose Length
Just because a cartridge fits in the magazine, does not mean that it will fit in the chamber. Features of a chamber are illustrated in Figure 12. The overall length of the cartridge must allow it to fit completely in the chamber without the bullet engaging the riflings. If the bullet engages the riflings before the cartridge is fully chambered, the slide will not lock into battery and the gun won’t fire, or runs the risk of firing out of battery, a potentially dangerous event. A critical feature is bullet nose length. Bullets with a short nose must be seated deeper than bullets with a long nose in order to fit with the same clearance of the riflings (see Figure 12).
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A realworld example of the maximum overall length that a bullet can be seated to and still fit in the chamber is shown in Figure 13. Six different bullet designs were seated until the cartridge was just able to fit in the chamber of a CZ 75 SP01 9mm barrel without the bullet engaging the riflings. The maximum overall length of each cartridge is shown just below the loaded cartridge. Each bullet design has a different maximum overall length. Note that the Hornady 124 FMJ RN bullet could be loaded to a length that exceeds the SAAMI maximum overall length of 1.169 inches (dashed line in Figure 13) for the 9mm Luger cartridge.
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Overall Length and Feeding Reliability
Careful bullet selection can benefit guns with reliability issues related to cartridge overall length. However, some gun designs are very particular about what they will feed, and if you’re loading the same bullet for multiple platforms, you might find that what feeds reliably in one gun won’t feed reliably in another. Here is a realworld example.
I loaded some 122 grain flat nose cast bullets for my 9mm Para Ordnance P189. The bullets had a short nose, and this Para Ordnance barrel had a relatively short throat, so I could load them no longer than an overall length of 1.022 inches. The Para Ordnance ran flawlessly with this load. However, when I tried this same ammunition in my CZ 75 SP01, it choked horrifically, and had a 76% feeding reliability rate. In many instances the bullet’s nose was jammed at the barrel hood and the cartridge base had slipped below the slide’s breach face and was pushed deep into the magazine, resulting in a cartridge that was nearly vertically oriented. Other rounds stopped just short of leveling out in the chamber.
I saw this as an opportunity to test bullet shape and overall length on feeding reliability in two different platforms. I selected several different bullet designs and loaded them at the same 1.022 inch overall length. A second group of ammo was loaded to lengths close to the “just fit” length for the SP01’s chamber. I loaded at least 100 rounds of each bullet type for each gun tested. (Methods: The rounds were loaded with bullet weight appropriate powder charges so that powder charge cycling issues did not confound the feeding reliability tests. I used two factory high capacity magazines for each gun and experienced no magazine specific reliability problems.) The results are shown in Figure 14.
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The test revealed that overall length is more important than bullet design for my SP01. The “round and hard” rule of thumb was trumped by overall length. None of the bullets tested ran 100% reliably in the SP01 when they were loaded to an overall length of 1.022 inches, though some ran more reliably than others. Also noted in Figure 14 is data showing how these same short loads functioned in the Para Ordnance P189. The Para Ordnance was not affected by the short overall length, with the exception of the Montana Gold 115 grain FMJ bullet. The Para experienced one feed failure with this load during the 100 round test. Even the most reliable guns will fail with ammunition that is too far out of spec.
I also tried the short loaded Montana Gold 115 grain FMJ rounds in a second CZ 75 (stainless). It also choked with a high failure rate, suggesting that the CZ 75 platform might be sensitive to short overall length. (Note that before I tried the short cast bullets in the SP01, it and my other CZ 75s ran flawlessly. CZs are excellent pistols and super reliable. They’re just picky about unusually short rounds. Other pistols might be, too.)
The second part of the test addressed whether some of these same bullets would feed reliably in the SP01 when loaded to an “appropriate” overall length. Two flat nose bullets (Hornady 124 grain FMJ FP and Montana Gold 125 grain FMJ SIG) were seated near their “just fit” overall length. The Montana Gold 115 grain FMJ RN bullet was seated a tenth of an inch longer (1.122 inches), but still some distance from its “just fit” length of 1.159 (see Figure 13). As before, 100 rounds of each load were fired through the SP01.
Reliability with the longer seated bullets was superb. Well, mostly. As shown in Figure 14, the SP01 still did not like the Hornady 124 grain FMJ FN. This example makes the important point that not all bullets are compatible with all guns.
Recall from Figure 13 that the Sierra 125 grain JHP bullet’s maximum overall length to fit in the chamber was 1.036 inches. This bullet has a short nose, and seated to that length, it is very close to 1.022 inches of the tested cartridges that feed so poorly. I loaded up what Sierra bullets I had (N=95) at 1.032 (allowing for a small margin of error for variations between individual rounds). The SP01 experienced no malfunctions with this load, but a few rounds had jerky forward slide movement, suggesting that they were close to a feeding malfunction. Note that this bullet has one of the widest flat noses available for a bullet of this caliber.
The data above suggest that flat nose bullets with a wide tip tend to feed more reliably than narrower nose bullets in this pistol when loaded to the same short overall length. This is shown graphically in Figure 15A. The profile of the Sierra 125 grain JHP bullet is shown when it is seated 0.010 inches farther out than the http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 18/20 4/12/2015 Bullet Design and Feeding Reliability others. The narrow nosed Montana Gold 115 grain FMJ bullet was the least reliable when loaded to 1.022 inches. All other bullets, all with wider noses, fed more reliably. The wide nosed Sierra bullet turned in a perfect score, albeit barely.
The nearvertically oriented misfeeding rounds suggest that overall length affected feed timing. For clarification, feed timing refers to the position of the slide as it moves forward to chamber a round. Feeding cartridges change angle twice. Once when the bullet nose hits the feed ramp where they angle upward, and the second time is when the bullet nose hits the upper inside of the chamber and the cartridge angles downward to straighten out and enter the chamber. If the slide is too far forward because of an especially short cartridge, the upward angle is too sharp and the cartridge can’t recover from that and straighten out to enter the chamber. In this experiment, bullets with a wider nose encounter the feed ramp and chamber earlier, with the slide farther back, resulting in sufficient time for the cartridge to change angle to enter the chamber.
The black bar in Figure 15B shows the approximate angle of the SP01’s feed ramp. This figure illustrates the relative difference in overall length that the bullets would have to be at to contact the feed ramp and maintain the same timing as the Sierra bullet. Note that the round nose bullets have a longer overall length than the flat nose bullets.
Figure 15B illustrates two main points. The first is that different bullet designs may require their own unique seating depth to regulate feed timing. Granted there is probably a range of overall lengths over which a given bullet will meet this timing requirement, and it can vary with gun design as shown by the difference in feeding behavior between the Para Ordnance P189 and CZ SP01 pistols in this example. The second point is that, when loaded to an equivalent overall length, wide nose bullets, round or flat point, will hit lower on the feed ramp than pointy bullets. In summary, this test has shown that multiple factors, overall length and bullet nose shape, can interact to influence feeding reliability. Summary
I hope that the information in this article will aid your search for a new bullet. Keep in mind that there are no “bad” bullets. We are blessed with an abundance of quality products to choose from. But design features of bullets and guns can affect reliability. It’s all about compatibility. Your results might vary from mine. It speaks to the differences in tolerances and designs between guns and a large number of variables that are sometimes difficult to account for. My approach to trying a different bullet is to assume it will feed reliably, and that it has to prove to me that it doesn’t. It’s the “innocent until proven guilty” approach. Check the http://38super.net/Pages/Bullet%20Design%20and%20Feeding%20Reliability.html 19/20 4/12/2015 Bullet Design and Feeding Reliability bullet manufacturer’s website for photographs if you’re looking for specific features.
Notes and Acknowledgements
1. Via email communication with Ty Herring, Barnes Bullets, LLC. The XPB or TACXP’s and the new Busters are made almost entirely by swaging, but the crimp groove is machined on the XPB and the TAC XP. The crimp groove on the Buster is swaged.
Norm Bjelland from Montana Gold Bullets notes that their 125 SIG bullet was designed to fit the 357 SIG feed ramp, and has a wider nose than most 9mm bullets.
Norm Bjelland from Montana Gold Bullets, kindly provided some sample bullets for this article.
SinterFire’s frangible bullets can be purchased at www.frangibleammo.com.
Round nose bullets for the .40/10mm: Plated: www.berrymfg.com; Cast: www.hunterssupply.com and www.lasercast.com.
References and Resources:
ANSI/SAAMI booklet Z299.31993. American National Standard. Voluntary Industry Performance Standards for Pressure and Velocity of Centerfire Pistol and Revolver Ammunition for the Use of Commercial Manufacturers. 1993. Sporting Arms & Ammunition Manufacturers' Institute, Inc., Wilton, Conn. USA.
Speer Reloading Manual #14 (2007) Lewiston, ID.
www.berrysmfg.com www.brass.org www.corbins.com www.frangiblebullets.com www.montanagoldbullet.com www.rainierballistics.com www.sinterfire.com
Questions, comments, suggestions, hate mail? Feel free to email me. However, the probability of getting a response is low simply because I have a day job and a life and don't have the time to respond to all emails. It's nothing personal, really. Nevertheless, I do appreciate your thoughts. If you see an obvious error then please put the word ERROR in the title of your email. Thanks, and happy shooting.
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