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Home , External ballistics, Muzzle rise

Internal and External The things you can’t see.

After the trigger is pulled on a , a lot goes on inside and outside the that you can’t see. Many of these invisible things are responsible for events you don’t normally think about.

Internal Ballistics

It starts with the firing pin or striker hitting the primer hard enough to cause it to detonate. The primer flash has to produce enough heat for a long enough period of time to ignite the ’s smokeless . In general, the brand of primers is not critical but it is a well-known fact that some match grade loads prefer a certain brand for optimum accuracy. A light-struck primer may still ignite the powder but it will not have as much flash as a primer with a full power strike, thus the cartridge will produce sub standard results. This becomes evident when you chronograph a string of 10 rounds and record the inconsistent velocities. As soon as the primer flashes, it will be thrust to the rear, pushed partially out of the pocket until it contacts the breech face. As the first few kernels of powder ignite, chamber starts building that pushes the forward and pushes case rearward to reseat the primer. Within a few thousandths of a second and an inch or so of bullet travel, chamber pressure and will peak, however this doesn’t mean the powder has completely burned up, it just means pressure will start dropping.

Next is the burn rate of the powder. Burn rate charts will tell you the order of burn rates from fastest to slowest when powder is burned in open air but don’t tell you what burn rate is optimum for your cartridge and bullet weight combination. Most reloading manuals do a good job of listing powders that are within acceptable burn rates. Burn rates can change radically depending on the volume of the cartridge and the weight of the bullet. The easiest way to burn rates is to determine how many inches of bullet travel it takes to totally burn up. Fast burning handgun powders such as Bullseye typically get a 100% burn in less than two inches of bullet travel. This makes fast burning powder a good candidate for low velocity target loads. Slow burning magnum powder such as W-296 will take about 15 inches of bullet travel to burn up. Because it takes so long to burn up, slow burning powder is best suited for magnum handgun velocities (1200 fps or faster) All powders are considered “slow burning” and take from 16 to 26 inches of bullet travel to totally burn up. As long as powder is still burning, it will create enough pressure to accelerate a bullet. This means a slow burning powder will push a bullet for a longer period of time, thus it will generate higher velocities than a fast burning powder and it will generate lower chamber pressure in the process. A software package named QuickLOAD will predict a given load’s parameters such as chamber pressure, velocity, bullet travel time, powder burn time, and many more. Although computer generated statistics in QuickLOAD are not as accurate as actual lab tests with real ammo, it does provide a reasonably accurate picture of when and what happens inside the chamber and bore When the powder’s burn rate best matches the weight of the bullet, the capacity of the case, and the length of the barrel, it will produce the best accuracy.

1 Burning powder accelerates at a rate of about 6000 feet per second (fps). As long as powder is still burning, it will push a bullet faster and faster, until the bullet finally exits the muzzle. Meantime, the bullet goes through several transitions. This starts as the bullet first begins to exit the case. It will contact the chamber throat (or cylinder throat). Chamber pressure will cause the bullet to expand slightly, causing it to seal in the bore. This process is called “obturation”, meaning to bump up in diameter until the cylinder or barrel throat restricts further expansion. As the bullet passes through the cylinder or chamber throat, it will be swaged (sized) to the proper diameter for the bore. In , the primary forcing cone is located in the mouth of the barrel and will guide the bullet into the bore. This transition is the most efficient when chamber pressure matches the hardness of the bullet to it to obturate and seal in the bore. For lead in handguns, the formula is: Bullet hardness (BHN) = chamber pressure divided by 1400. Jacketed bullets also obturate but require considerably more pressure. Handgun jacketed bullets have a thinner and softer jacket so chamber closest to the SAAMI max rated pressure for the cartridge seem to be the most accurate. Most rifle chamber pressures are in the range of 50,000 psi, which will force a thick jacketed rifle bullet to obturate. With jacketed bullets, you are at the mercy of the manufacturer to make bullets with the proper jacket thickness and hardness. As such, you may find some reduced power loads using jacketed bullet don’t work very well.

A bullet’s “ogive” is the diameter where the bullet first contacts the throat. As an example, the ogive for a round nose .308 bullet would be where the diameter is about .296”. The of the throat may not be friendly with the angle on the bullet’s ogive. This is one of the many issues that can cause a rifle to be “ammo fussy”, where one type of bullet is far more accurate than anther type. Assuming a friendly throat contact, there will be minimum bullet damage. Bullet seating depth is very important because the bullet has already increased in velocity by the time it strikes the throat. Too much pre-throat bullet travel will cause higher velocity and excessive bullet strike damage, which will affect accuracy. Too little pre-throat bullet travel will increase chamber pressure, possibly to dangerously high levels that can damage the gun. Pre-throat bullet travel is controlled with bullet seating depth. Using the reloading manual’s COL is highly recommended.

The bullet contacts the lands and grooves in the bore called “rifling”. This will engrave the bullet with a reverse image of the rifling. In other words, the lands that extend from the bore will create grooves in the bullet and the grooves in the bore will create lands on the bullet. The engraving process takes considerable starting chamber pressure …. more for jacketed bullets, less for lead bullets. Once the bullet has been engraved and is pushed down the bore by rapidly expanding gasses that create chamber pressure, a seal will be established between the bullet circumference and the bore. Because lead bullets are much softer than jacketed bullets, pressure keeps them expanded so they tend to seal much better in the bore and result in higher velocity than an equal powder charge pushing a equal weight jacketed bullet. Bullet to bore friction becomes negligible when a fractional ounce bullet is being pushed by several tons of pressure.

While the bullet is transitioning through the bore, the rifling twist rate combined with the bullet’s will cause to bullet to spin very rapidly to maintain downrange stability. Rifling twist rates are expressed in a ratio such as 8:1. This would mean the bullet spins one complete revolution in every 8 inches of travel. The bullet’s spin rate can be determined with the following formula: Spin rate in RPM = 12 divided by twist rate, times muzzle velocity, times 60. As an example, lets say a 223 Rem bullet exits the 2 muzzle at 3240 fps and the barrel has a 1:9 twist rate. 12/9=1.333 X 3240 = 4320 X 60 = 259,200 RPM. Bullet spin will create torque while inside the bore and will actually twist the firearm enough to be seen and felt by the shooter. A heavier bullet combined with a faster twist rate will increase barrel torque considerably. This sudden twisting of the firearm can wreak havoc with accuracy. Typical handguns have a slow twist rate for this very reason. Longer shooting distance is not an issue like it is with a rifle so the rifling twist rate in a handgun is much slower to accommodate larger diameter heavy bullets and prevent excessive barrel torque.

The pressure generated by burning powder in conjunction with the mass and length of the barrel will cause the barrel to vibrate. Because of the rifling, barrel vibrations tend to make the muzzle move in a circular motion in the same direction as rifling. This phenomenon is commonly called “barrel harmonics” and only applies to because handgun barrels are normally too short to be affected by harmonics. As a bullet moves closer to the muzzle, the frequency generated by the vibrations increases …. much like pulling the slide closer on a slide trombone will increase the frequency (higher pitch notes). From the true meaning of harmonics, frequencies will add algebraically to produce a very complex waveform. A modest difference in muzzle velocity will change the waveform and make the end of the muzzle rotate at a different rate. As the muzzle rotates from harmonics, it will result in bullets being launched at slightly different . This will show up on a target as a group of holes rather than one single hole. The less harmonic control you have, the larger the group will be. The single biggest harmonic contributor is longer thinner barrels. The countermeasure for barrel harmonics is to prevent the barrel from vibrating. This can be done by replacing the barrel with a heavy bull barrel or it can be done by bedding a to contact the barrel in a manner where vibrations are dampened. Other techniques involve a product called an “Accu Strut” that is commonly used on Ruger Mini-14s to help prevent the pencil barrel from vibrating.

In addition to muzzle rotation, if the combined barrel harmonics just happen to peak at a location where the stock touches the barrel, it will cause the barrel to “push off” from the stock. This will always result in groups that are higher than center …. never lower because the stock prevents the barrel from moving down but groups could be left or right of center. Using a sling may have the same “push off” effect because the sling pulls the stock to the side and pull the barrel along with it.

Free floating a barrel is just the opposite of dampening (ie bedding). It allows the barrel to float without touching the stock, which will totally prevent “push off” and is a much better solution when a sling is used …. assuming the stock is never pulled far enough to contact the barrel. If the ammunition is high quality and produces uniform velocities, barrel harmonics will be very predictable, thus excellent accuracy is achievable. If ammo does not produce uniform velocities, accuracy will be poor due to harmonic muzzle rotation . Many people free float their barrels and are sadly disappointed with the results because they don’t use high quality ammo with uniform bullet weights and powder charges. Bedding a stock is less fussy and usually delivers decent accuracy no matter what ammo is used.

Another countermeasure for barrel harmonics is using a shorter barrel. Most barrels taper so if a 24” barrel is cut down to 18”, it will be short enough and massive enough to prevent or at least minimize the affects of barrel harmonics. Of course a shorter barrel will not develop as much velocity so there are always tradeoffs. Another profitable side 3 affect of a shorter barrel is, powder will not get a complete burn …. in fact only x-amount of powder will burn so the shorter barrel tends to regulate velocity much better than a longer barrel. Long range shooters need the extra barrel length to develop more velocity whereas a big game hunter will find a shorter barrel will still kill Bambi at 250 yards. Further, short barrels are much easier to handle in the field … especially in thick brush or dense woods. Even 22 LR rifles suffer from barrel harmonics. An interesting test is to shoot a 10” barrel Ruger Charger against a normal 10/22 with a 18.5” barrel. Although velocity will be lower with the Charger, likely the Charger will be more accurate at 50 yards…. all because the shorter barrel has less influence from harmonics.

As a bullet exits the bore, the barrel’s crown comes into play. The purpose of the crown is to provide equal exit pressure on the entire circumference of the bullet’s base. Should the crown get damaged ever so slightly, more pressure will be exerted on one area of the bullet, which will cause it to be blown slightly off course, thus larger groups. Crowns tend to have more influence on lighter and faster bullets than heavier or slower bullets. That’s because its easier to divert a lighter bullet and also because there is a considerably stronger with higher velocity bullets.

External Ballistics

Bullet spin creates a gyro effect, meaning a spinning object tends to stay in the same plane like a spinning toy top. A good example would be a spinning bicycle wheel. If you hold the axel on both sides and try to turn the wheel right or left, it is very difficult and the faster the wheel spins, the more resistant it is to turning. The larger the diameter of the spinning object, the more gyro effect it will generate. As applied to bullets, larger diameter bullets generate more gyro effect so they don’t need to be spun as fast to maintain stability. Small diameter bullets such as 22 cal or even worse, 20 or 17 cal bullets must be spun very fast to keep them stable. This concept just happens to work out quite well because lighter (smaller diameter) bullets can be launched at very high velocities whereas heavy large bullets typically have a much lower muzzle velocity.

Bullet spin is very important because there are no wings or fins on bullets so spin is the only thing that keeps a bullet stable in flight. With very few exceptions (ie hollow base wad cutters), bullets have a lighter nose and a heavier base. This makes the bullet want to “swap ends” in flight, much like throwing a dart tail first. As long as the spin rate generates enough gyro effect, the bullet will continue downrange with the nose pointing forward. As the spin rate decays from air friction, the bullet will start to yaw …. meaning the nose will be pointed in some direction other than perfectly straight forward. When the bullet yaws, it also increases air friction so the bullet will slow down even more until it wobbles and finally starts to tumble. Depending on the bullet’s BC and spin rate, this could be under 50 yards with a handgun to 1500 yards or more with a very low rifle bullet. Bullet design is very important for downrange stability in rifles. When the bullet’s center of is closest to the actual center of the bullet, it will be much more stable in flight. Probably the least aerodynamic bullet known to man is a dual ended wad cutter (DEWC). However, because the bullet is almost a perfect cylinder, its nose and base weigh the same. This means the bullet will not try to swap ends in flight. In fact a DEWC will maintain stability as long as it is airborne … no matter how far that may be.

4 Imperfections will also cause bullets to be unstable downrange. In general, anything that causes bullet damage is going to affect its balance or BC. This could be scratches, dings, or damage from feeding. In the bore where one or more lands or grooves are a different depth, the bullet’s balance will be affected so the bullet will become unstable at a closer shooting distance. This is a very common issue with inexpensive 22 LR rifles that have inferior barrels. Most 22 LRs will maintain decent accuracy out to 60 or 70 yards but groups will then open up due to bullet imperfections from faulty rifling and poor quality bullets. Further, an inconsistent bore that has constrictions or bulges will also cause bullet damage and will show up on a target as consistently poor groups. When the spin rate no longer supports the bullet’s stability, the bullet will cut oval holes in the paper target and just a few yards farther, ovals will turn to keyholes. Any time you see oval or keyholes in a target, it means the bullet has destabilized. Of course, just a poor quality bullet can cause the same accuracy issues. It is common to see air bubbles or voids in cast bullets just as it is common to see variation in jacket thickness in cheap FMJ or JHP bullets. These conditions will make the bullet unbalanced and will have a direct impact on accuracy. Basically, anything that results in an imperfect bullet leaving the muzzle can account for poor accuracy and/or downrange instability.

As soon as the bullet fully exits the bore, a strange phenomenon takes place that converts bullet torque in the bore to centrifugal force in the air. Centrifugal force will cause the rapidly spinning bullet to develop a spiral path …. much like a corkscrew as viewed from behind the shooter where the spiral is the largest diameter and gets progressively smaller as the bullet travels downrange. So now the bullet is zooming downrange …. spinning very fast and spiraling …. two separate motions. This will continue until the spiral fully dissipates, leaving the bullet still spinning. The diameter of the spiral is determined by the length of the bullet (in relation to its diameter) combined with the bullet’s spin rate. Long skinny bullets with a fast spin rate can easily develop a spiral twice the bullet’s length. Long-range shooters call the point where the centrifugal force spiral dissipates “going to sleep”, meaning after this distance, the bullet will continue on a predictable path with no spiral. Meantime, the bullet’s path while in the centrifugal force spiral will cause groups to be larger at closer distances than at longer distances. This is counterintuitive but it really happens …. especially with rifles shooting high velocity long bullets. It is not unusual to see 100 yard groups print 2 inches whereas the same load prints an inch at 200 yards. This phenomenon has spoofed many shooters, making them think their rifles were not accurate when indeed the bullets had not yet gone to sleep.

As noted above, longer bullets launched at higher velocities tend to have large centrifugal force spirals and as such, it takes a longer distance for the spiral to dissipate. 22 LR bullets are short and exit at a low velocity from a slow twist rate so the centrifugal force spiral is very small in diameter and dissipates before the bullet travels 25 yards. 55 gr (or lighter) .224” bullets used in many centerfire cartridges are also quite short and typically will recover from the centrifugal force spiral in 75 yards or less. Longer (and heavier) .224” 62gr bullets will go to sleep at about 125 yards. This tends to make 55gr bullets a little more accurate at closer distances and heavier bullet with a higher BC more accurate at longer distances. Very low drag (VLD) .224” bullets in the 70~77 gr weight class may take as long as 225 yards to go to sleep. Conventional bullets used in high power big game hunting loads typically have a modest BC in the .3~.4 range …. high enough where the bullet will maintain stability well past normal hunting distances. These bullets tend to travel up to 150 yards before they go to sleep so judging accuracy at 100 yards may not reveal the true accuracy. VLD larger diameter bullets are specifically designed for long 5 range shooting, 1000 yards or even more. These bullets can take up to 300 yards to dissipate the centrifugal force spiral. A big mistake many shooters make is to buy VLD bullets for closer distance shooting. Because the spirals are quite large in diameter, these bullets tend to group poorly until after they go to sleep. So …. the concept for determining the most accurate bullet for your needs should include the intended distance where shorter (lighter) bullets tend to be more accurate at closer distances and longer (heavier) bullets are more accurate at longer distances.

A term called “over stabilized” is often used. This means a bullet is being spun so fast that a large centrifugal force spiral has formed. When bullets are over stabilized, accuracy at closer distances is poor but long range accuracy will be good, once the spiral dissipates. This effect is common with long rage rifle accuracy and oddly enough, some handguns. For example, a 9mm Luger pistol typically has a very fast twist rate of 1:10 where other bullets in similar diameters have a twist rate of 1:18. This over stabilization issue causes a 9mm Luger’s accuracy to suffer until the bullet goes to sleep at about 25 yards, so don’t expect tight groups when shooting at 25 yards or less.. With long range target rifles, over stabilization is a common technique used to keep the bullet spinning as fast as possible and extend the stabilized shooting distance. Of course these rifles are not used at closer distances where the spiral is still prominent.

Once the bullet starts traveling downrange, its path is primarily determined by the bullet’s ability to deal with air friction. This rating is called the bullet’s “” (BC), which is based on “1” being a perfect bullet with no influence from air friction. Bullets can have a range of BCs from less than .1 to more than .6 …. the larger the number, the more aerodynamic the bullet will be. The bullet’s weight is somewhat counterintuitive because heavier bullets tend to have higher BCs so they actually drop less than lighter bullets at the same shooting distance. Gravity pulls at a rate of 32 ft/sec/sec no matter what the bullet weighs so bullet drop is based on how long the bullet is exposed to gravitational pull.

“Time to target” is an ever increasing amount of time it takes the bullet to get to its destination. One would think it would take twice as long for a bullet to travel 500 yards as it does to travel 250 yards … close but not true. Why? The bullet slows down based on air friction so each yard of travel takes a slight bit longer than the previous yard of travel. Using a 223 Rem as an example, it takes about .1 seconds for the bullet to travel 100 yards, about .23 seconds to travel 200 yards, .38 seconds for 300 yards, .73 seconds for 500 yards and finally …. 2.2 seconds for 1000 yards. The reason why time to target is so important is …. the longer a bullet is exposed to gravity, the more it will drop. The same goes for drift and spin drift …. a longer exposure time will make a proportionally larger drift error.

As a bullet moves through the air, air friction will cause the bullet to slow down at a predictable rate. It will also cause the bullet’s spin rate to decay. In other words, at some point down range, when a bullet has lost considerable muzzle velocity; it has also lost a proportional amount of spin rate. Once the bullet’s spin rate drops below the point of gyro stability, the bullet will start to wobble then a bit farther downrange it will begin to tumble. By this time, accuracy has gone down the tubes. Further, wind will make the bullet drift off course at a predictable rate. Wind drift is directly correlated with BC, no matter what direction it comes from. At a given shooting distance, a 20 mph wind will cause a bullet to drift exactly twice as much as a 10 mph wind from the same direction. 6 Ballisticians use “drag tables” to predict the effects of bullet drop with ballistic coefficient. The normal drag table for sporting arms is G1. There are many other drag tables for different …. none of which are perfect but are close enough to predict bullet drop at considerable distances. Ballistic coefficients aren’t perfect either, in fact the formulas for BC were developed long before computers and VLD bullets so there are now a few large caliber bullets that exceed the perfect BC of “1”.

Bullets have an advertised BC but the wind tunnel tests done to determine BC uses a virgin bullet with no engraving. This means BCs are never quite as good as advertised. I don’t think bullet manufacturers are trying to dupe us …. they just don’t know the type and depth of rifling used in your specific gun. Ballistic Explorer software has a feature for computing actual BC. It amounts to chronographing loads at 4 yards and again at 100 yards. The average velocity results from both distances are then plugged into the software to determine actual BC in your specific rifle with your specific ammo. Once an actual BC has been determined, the ballistic charts developed by Ballistic Explorer are very accurate …. virtually identical to results developed from actual shooting at a range.

The next rifle phenomenon is called “spindrift” which is also related to the bullet’s BC and the bullet’s spin rate. As it turns out, the bullet’s BC coupled with air friction, the bullet will act like a miniature impeller. With the influence from engraving, the “impeller action” slows the bullet and it also causes the bullet to arch left or right in the rotational direction of bullet spin. To put this into perspective, assume a bullet path at 100 yards is dead on target. At 300 yards, a 30-‘06 bullet spindrift will cause the bullet to impact an inch to the right (assuming normal right hand rifling). At 500 yards, the bullet’s spindrift will be about 3” right, and at 1000 yards spindrift will be about 25 inches right. Although this sounds like a huge amount, it is really only about 2.5 MOA. The reason why spindrift is more dramatic at longer distances is simply “time to target”. If a bullet did not have rifling engraving, it would have way less spindrift. Remington makes a 30- ’06 cartridge called an “Accelerator”. It has a .224” 55gr FMJ bullet in a Teflon . Once launched, the sabot drops away leaving a virgin 55gr bullet going down range at in excess of 4000 fps. In theory, the bullet’s super fast spin rate should cause considerable spindrift, however because there is no rifling engraving, spindrift is very minimal. When bullets get corroded, the extra air friction will increase spindrift.

Sonic transition is when a bullet goes from being supersonic to subsonic. This is a velocity of about 1155 fps and will change with air density, altitude and barometric pressure. For many years, it was thought that bullets became unstable after transitioning from super to sub sonic. As it turns out, this concept has been taught by many authorities and was thought to be proven. This concept was proven false in more recent years, but many people still cling to old false information. Back in the 1960s, there were a lot of jet aircraft being developed that could easily exceed the of sound. Some of these aircraft became very unstable when they transitioned from super to sub sonic so aircraft engineers had to find and fix the problem. Somehow, the sonic transition technology got transferred to bullets. Never mind the fact that a bullet doesn’t have wings or any other attributes that cause instability. In about this same time period, the M-16 / AR-15 rifles were being developed. At first, they has a slow 1”12 twist rate and fired a standard USGI M-193 cartridge with a 55 gr bullet. The bullet had BC of about .15 which is very poor for a rifle. Turns out, these bullets were launched from a 20” M-16 barrel at about 3000 fps. By the time a bullet reached about 250 yards, it started becoming unstable, which 7 was indicated by oval holes in the paper targets and by 275 yards, the holes in the targets resembled keyholes. By total coincidence, this happened at the same distance as when the bullet passed through sonic transition so it was proclaimed to be sonic transition that was the cause for bullets going unstable.

Many years later, a man named Gail McMillan set out to disprove this theory. Gail was a professional long range shooter with his office walls decorated in certificates, trophies, and even world records. He held the “tightest group” world record for several years. Gail was also one of the very best rifle barrel makers at the time so he really knew his business. To prove the point, Gail had two Remington 700 rifles, both chambered in 223 Rem. One had the standard factory twist rate of 1:12 and the other had a McMillan made barrel with a 1:10 twist rate, both were 24”. At the range, he used exactly the same M- 193 cartridges for both (55gr bullets). A chronograph was set up at 250 yards and both rifles recorded virtually identical velocities just over the , (1175 fps). Both guns fire respectable groups of 2.5” at 250 yards. The target and chronograph was then moved to 275 yards where the gun with the 1”12 twist rate failed miserably with all bullets creating ovals or keyholes in the target. Meantime, the gun with the 1:10 twist rate was still producing nice round holes in the target and were still grouping tight. The point being; a faster spin rate kept the bullets stable well past the sonic transition, proving it was a decaying spin rate, not a sonic transition that caused the bullets to destabilize.

So, the theory was debunked …. What really caused bullets to get unstable at distances beyond 250 yards was the spin rate had decayed from air resistance, enough where the bullets were starting to yaw and tumble. To this day, many people still believe the sonic transition concept because it was propagated throughout the shooting industry. Many different cartridges follow the same path …. by coincidence, they lose stability at about the same distance as when they go subsonic. A similar rifle with a faster twist rate will prove the point because bullets at the same downrange velocity but with a faster spin rate will maintain stability for a longer distance.

To fight this downrange instability issue, a couple things have happened. First, manufacturers now off faster twist rate barrels in most popular chamberings. Second, bullet manufacturers now offer very low drag (VLD) bullets that have a much higher ballistic coefficient, thus they will maintain velocity and stability for a longer distance.

There is a strange force at work that can affect a bullet’s path. It is called the “Coriolis Effect” and is based on the rotation of the Earth. At distances of 400 yards or less, it has less than a 1” influence on the bullet’s path but at longer distances, it is a force worth reckoning. This little known effect causes a bullet to drop a little faster when shooting west and drop not quite as fast when shooting east. When shooting north, the bullet will strike slightly left of the target and if you are shooting south, the bullet will strike slightly right of the target This strange effect is more pronounced as you get closer to the equator and less pronounced as you get closer to the north or south pole. The Earth rotates clockwise (west towards the east) moving at about 1041 mph (1500 fps) at the equator or about 1050 fps in the USA. The atmosphere moves with the earth’s rotation so it convolutes the formula so basically it means a bullet has to travel slightly farther and take slightly longer to reach its destination when fired in a westerly direction. It works much like a headwind when shooting west or a tail wind when shooting east. Likewise, an east wind when shooting north or south. This goes back to the old “time to target” concept where more exposure time means gravity will pull the bullet down more or wind will 8 cause more wind drift. The Coriolis Effect only affects long range shooters and is not a consideration for hunters. Better ballistics software programs such as Ballistic Explorer include and shooting direction parameters for computing the Coriolis effect.

More common sense issues that affect a bullet’s are , temperature, wind direction & speed, altitude, and range slope. Basically, any condition that makes the air denser will increase friction on bullets and make them lose velocity more rapidly and drop more. These would include: lower altitude, higher barometric pressure, higher humidity, and lower temperature. Range slope is not intuitive … shooting either uphill or downhill requires aiming a bit low because there is less gravitational pull than when shooting level with the earth. Wind direction is not always intuitive. A headwind or tailwind will have minimal effect on a bullet’s path, however it doesn’t take much side wind to blow a bullet off course. As an example: 1 mph=1.466 fps so a 10 mph headwind would be 14.66 fps. Assuming a BC of .5, this would lower the bullet’s velocity by about 7.33 fps. The same would be true for a tailwind only it would increase the bullet’s velocity by 7.33 fps, which is not even noticeable. A 10 mph 3 or 9 o’clock side wind will drift a 30-’06 bullet by a half inch at 100 yards, 5” at 300 yards, and 15” at 500 yards.

Handguns: The normal shooting distance for most handguns is 25 yards or less. In some cases, handguns can be effective out to 50 and maybe even 100 yards…. but typically, handguns are designed for much closer shooting distances. The goal for target grade handguns is a 1 inch group (or less) at 25 yards, which is 4 MOA. Snubby revolvers or small easily concealable self-defense handguns are hard pressed to get a 2” group at 10 yards (20 MOA). As a result, many of the “accuracy issues” for rifles don’t really apply for handguns. As noted previously, “time to target” is a critical factor, however with handguns and close shooting distances, things like ballistic coefficient, temperature, humidity, and wind drift make very little difference when the distance and time to target is so short.

Most handguns have a very slow twist rate to help counter barrel torque yet provide enough spin to keep the bullet stable through its useable range. Heavier bullets cause considerably more barrel torque so twist rates for larger and heavier bullets are even slower than those with smaller diameter bullets. Larger diameter handgun bullets launch at much lower velocities than most rifles so even a slow twist rate will keep handgun bullets stabilized for 50 yards or more …. well past normal shooting distances. Seems each cartridge has a factory standard twist rate that is common throughout the shooting industry. Many of these standards date back to the turn of the last century when smokeless gunpowder was being developed. As an example, the twist rate for a 38 Special has been an oddball 1:18 3/4 for more than a century. When the 357 Mag was introduced, it used the same odd ball twist rate. With a typical velocity of 850 fps, the 38 Special bullet is only spinning at a rate of 32,640 RPM, a far cry from 259,200 RPM, in the 223 Rem example above. A 44 Mag typically has a twist rate of 1:20. This is slow enough to prevent excessive barrel torque and fast enough to keep bullets stabilized for at least 100 yards at magnum velocities. One handgun exception is the 9mm Luger. The original Luger pistol was designed where a stock could be attached to make the pistol into a longer range of sorts. The twist rate was set at 1:10 to keep bullets stabilized at longer distances and is still the same more than 100 years later. Most 9mm pistols with a 1:10 twist rate will keep bullets stabilized to 150 yards or more. That said, the centrifugal force spiral is large enough at closer distances (under 25 yards) 9 where 9mm groups tend to scatter. 9 mm pistols are still plenty accurate for their intended purpose of self defense.

Most accuracy issues with handguns are things you can see but only a few follow rifle trends, such as bore conditions and bullet damage. You can see a corrupted forcing cone, a badly fouled barrel, or cylinder throats that are too tight, which all have a direct impact on accuracy. There is a huge span of powder burn rates for handgun loads so selecting the optimum burn rate and bullet weight versus barrel length and bore diameter will improve accuracy considerably.

Recoil begins as soon as powder starts to burn. Rifles tend to straight back and have minimal effect on accuracy. Handguns are a different story because they are shaped more like the letter “L”. This forms a right angle lever so when the pistol or revolver , the barrel will push back and because the grip is held firmly, the corner of the “L” becomes a pivot point causing the muzzle to rise. Muzzle rise happens in virtually all handguns …. even 22 LRs, although minimally. Because the muzzle rises before the bullet exits the muzzle, it will have a direct impact on vertical shot placement. If you lay a long straight edge (such as a yardstick) on top of the , you will see the sights are aimed considerably higher than bore line. A laser bore sighter is even more dramatic. If you aim the handgun at a target, the laser dot will be several inches below the iron sight’s point of aim. When a handgun is fired, the muzzle will rise until the bullet intersects with the sight line. The process of calibrating a gun for muzzle rise is called “sight registration” and is done at the factory by adjusting the front sight height and using the most common load for the specific gun. Basically it calibrates how much the muzzle has to rise to make the bullet hit the bullseye. To make sight registration work, you need to have a firm hold on the grips … not a death grip and certainly not a wimpy grip. Once you master grip tension and sight picture, your shots should hit in the bullseye. Heavier bullets tend to be launched at a lower velocity and typically generate more recoil. This makes the dwell time in the bore longer and gives the barrel more time to rise. In short …. heavier bullets will strike the target higher than normal weight bullets and lighter bullets will strike the target lower than normal. This is a perfect reason why many handguns have adjustable sights.

As noted above, rifles tend to recoil straight back. That said, when a rifle is fired, there will be a considerable muzzle blast as pressure is released from the bore. This can cause the muzzle to rise but because it happens after the bullet exits the muzzle, it has no impact on accuracy. Muzzle blast also happens with handguns …. especially magnums. Although muzzle rise from recoil does make a handgun shoot higher, muzzle blast itself has no impact on accuracy …. just a lot of noise and a big flash. Many handgun shooters try to compensate for muzzle blast by pulling the muzzle down while they are squeezing the trigger… only to end up shooting low.

Muzzle flash is mostly just an annoying property of gun powder. In military applications, a rifle’s muzzle flash will allow the enemy to locate the shooter so a flash suppressor is used to divert the flash, making it more difficult to see where it is coming from. For handguns, most shooting is done in daylight so muzzle flashes are not a big distraction. When you shoot at an indoor range or in subdued lighting conditions, muzzle flash can temporarily blind the shooter. There are a couple ways to deal with muzzle flash from handguns. You can use powders that have flash suppressants added or you can deal with muzzle flash with a little training and practice. The procedure is to take aim, start 10 squeezing the trigger and just a fraction of a second before the sear releases, blink your eyes. This will block out the very fast muzzle flash and you will be able to see normally afterwards.

Virtually all types of gun powder will generate a muzzle flash. Some flashes are so subdued they don’t show up except in near total darkness. The worst muzzle flashes come from magnum revolvers that use slow burning powder. These powders can take at least 10 inches to as much as 15 inches of bullet travel to burn up. If the barrel is shorter than the distance for a total burn, some of the powder will be blown out of the muzzle where it will ignite and generate a large muzzle flash. It is not unusual to see a 3 foot long muzzle flash plume from a magnum revolver. The shorter the barrel, the larger the muzzle flash. The good news is …. magnum revolvers are usually used for daylight hunting or target shooting and are not commonly used at night.

Muzzle brakes can be very effective by using the high pressure muzzle blast to divert the muzzle in a different direction. There are two main types … one type for handguns vents upward through slots in the barrel. This will counteract muzzle rise and make second shot recovery much easier. The second type directs the muzzle blast to the rear, counteracting and reducing recoil. These muzzle brakes can be used on a rifle or handgun to tame recoil considerably. One thing about recoil muzzle brakes …. the gun’s report is very loud for anyone standing to the side of the shooter and even the shooter will get a much louder report. Ear protection is always required with muzzle brakes.

The next type of suppressor is designed to help reduce the sound level of the report. These are commonly known as “silencers” but only in the movies do they truly silence a firearm. What a really does is act just like a miniature muffler. Inside the silencer there are diversion plates that break up the sound. In the more hi-tech units, they are made like an audio wave-guide where pressure is diverted then directed back on the source. This is like mixing a positive sound with a negative sound, which cancels out much of the noise so the exiting sound is a fraction of the original. Silencers are rated in decibels (db) of attenuation. Each 3 db increase doubles the sound level. A really good suppressor will provide about 25 db attenuation. The unaltered sound level of a 22 rifle is about 140 db and an average of 165 db for 30-’06 rifle. If a 25 db suppressor was used on the high power rifle, the report would sound about the same loudness as a 22 rifle. This is still loud but nothing to compare with an unaltered high power rifle. Silencers (sound suppressors) are getting more popular nation wide and hopefully they will be removed from the Class III tax stamp requirements. BATFE keeps close tabs on who owns silencers and controls them individually by serial number. It cost $200 for a Federal Class III tax stamp for a suppressor plus a good suppressor could cost well over $300. The cost alone makes owning a suppressor just about impossible for most citizens, not to mention a several month wait for BATFE approval.

Finally, we are getting to the nuts and bolts of things. Considering the effects from all the above influences on a bullet’s path, it a wonder a bullet can hit the target at all! Putting most of the above issues aside, we find simple common sense solutions for complex issues. If the bullet drops too much, just aim a little higher. If the bullet strikes left of the bullseye, just aim a little right. The challenge is to hit the target with the first round.

Ballistics charts are great for determining how much you have to hold over (or under) at a given distance to hit the target. Obviously the first step is to set a reference point …. a 11 fancy way of saying “sight the rifle in at x yards”. Once a reference point has been established, let the computer do the work while the shooter reaps the benefits.

Seems most people in the shooting industry tend to compare rifles with a 30-’06 so why be different. The following ballistics chart is for a 30-’06 with a 180gr bullet (BC=.503) and a muzzle velocity of 2700 fps. The point of reference (sight-in distance) is set at 200 yards. Keep in mind, this is more of a generic ballistics chart because other cartridges with different ballistic coefficients and different muzzle velocities will chart different.

Ballistic Chart

The horizontal blue dotted line is the “sight line” as viewed through a scope. The numbers on the left side (6” increments) indicate how many inches above or below sight line the bullet will strike and how many inches the scope is mounted above bore line. The red arched line is the bullet’s path from the muzzle (0 yards) out to 500 yards. The yardage markers from 0~500 yards can be used to determine where a bullet will strike at a given distance. The first thing to note is the bullet starts off 1.5” low because the scope is mounted where the center of the scope is 1.5” above the center of the bore. The rifle’s muzzle must be pointed up slightly to make the bullet path intersect with the sight line. For this specific load, the bullet crosses the sight line at 30 yards and continues on a slight upward path until it peaks at +2” at 120 yards. At this point, the bullet will start dropping due to gravitational pull. At 200 yards, the bullet again intersects with the sight line and as it travels even farther, it will continue to drop at an increasing rate until the chart runs out at 500 yards with a 48” bullet drop. 12

As you can see, the trajectory is pretty flat from the muzzle out to 235 yards, never more than 2” high or 2” low. We can use this trajectory “channel” to our advantage when hunting. The +or- 2” channel will place a bullet well into a big game 8” kill zone at any distance out to 235 yards by just aiming directly at the target …. no hold over or hold under, just a “point blank” aim. By the way, for most hunters, 225 yards is the maximum distance for a clean kill. Yes, a 30’06 will likely kill a deer at 500 yards if you, the rifle, and the ammo, are precise enough for kill zone shot placement. Ever wondered why 3~9X scopes are so popular? Turns out 1X magnification for each 25 yards is optimum for hunting big game. This makes a good optical kill range from 75 to 225 yards that matches the rifle’s trajectory and typical hunting conditions.

For precision the above chart may not be quite precise enough so Ballistic Explorer will allow you to change the distance and display only the first half or the second half of the total distance. This can make each large square .5” or 1” instead of 6” in the above chart. Further, ballistic charts can be generated with the max distance of 25, 50, 100, 250, 500, 1000, 2000, and 2500 yards or meters. This will cover virtually any gun from a 22 short handgun to a 50 BMG rifle.

Ballistic charts are computed based on several inputs such as muzzle velocity, zeroed range, sight height, ballistic coefficient, bullet weight, altitude, barometric pressure, temperature, humidity, wind speed, wind direction, range slope, barrel twist rate, bullet length, bullet diameter, direction you will be firing and finally, your latitude. Some of these are default values or they can be changed for specific conditions. In addition to the graphed chart, you can also produce a Trace Chart that contains the computed outputs. These can be organized in 1, 5, 10, or 25 yard range increments. So if you want to know the bullet’s velocity or any other parameter at X yards, all you have to do is look at the spreadsheet. The following is Trace Chart for the above 30-’06 load in 25yard increments out to 500 yards with a 10 mph wind from 3 o’clock.

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The first column “Drop” assumes the barrel is level with the ground … not pointed up. Path is indicated in the graphic chart as the red line. Zero Adj MOA is the amount of sight correction needed at a specific range (in minutes of angle or MOA). This means you could do about a 4 MOA holdover and be very close at 350 yards. Here’s a Ballistics chart for a 223 Rem similar to what I use when I go prairie doggin’. It is not unusual for a prairie dog to peek out of their hole where you have a target about the sized of a quarter. This means your rifle and ammo must be pretty accurate and it also means a more detailed chart is needed. I use a laser range finder to determine the target distance, then look at my ballistic chart to see what my holdover or holdunder will be. Let’s assume I found a target at 150 yards as marked by the crosshair. With my rife zeroed at 175 yards, I would have to hold .58” low.

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Note the inch markers on the left are in ½” increments which makes it easier to correlate distance with holdover or holdunder. Out to 250 yards, my rifle and ammo are accurate enough to get one shot kills most of the time. On the longer shots, wind can really do a job on you so I shoot once with a dead on aim and watch for the bullet to hit. I then adjust and accordingly and usually connect on the second shot providing the prairie dog didn’t run down his hole. I always leave my crosshairs set at the sight in distance then simply use my charts. When I first get to the prairie dog town, I’ll set up a target and tweak my scope for a 175 yard zero. This takes the guesswork out of compensating for temperature, humidity, altitude, etc. I’m not shooting far enough where spindrift or Coriolis Effect will have a much impact.

Prior to printing up ballistic charts to take with me on a prairie dog hunt, I use Ballistic Explorer and my chronograph to determine my exact BC and velocity for the load I’m going to use. In this case it is a 55gr Nosler Ballistic tip bullet with 26.5gr of Varget in a LC 5.56 NATO case with a velocity of 3200 fps. The book says the bullet’s BC is .267 but my chronograph says its .244. This slight difference is hardly noticeable until you get to 200 yards, then it does start making a difference. This system has worked exceptionally well for me. Most of the time its one shot – one kill. I take a nifty wind meter (anemometer) and a wind drift chart with me and use it to compensate for wind drift.

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The above chart is use to determine wind drift. It was set for a 10 mph at 3 o’clock. Because winds are so proportional, you can use this chart for most any wind speed and even direction. Example: lets say you spot a target at 150 yards and the wind is blowing from 3 o’clock at 10 mph. Your bullet would drift left by about 2”. If the wind reduced to 5 mph, the drift would be 1” left. If the wind was 10 mph but changed direction and came from 4:30 o’clock, it would reduce bullet drift by about half, resulting in a 1” left drift. As you can see, the longer a bullet is exposed to wind, the more it will drift. Just a light 10 mph breeze will drift the bullet 6” off course at 250 yards, making it very difficult to hit a “quarter” sized prairie dog target.

To take advantage of ballistics charts, you need a decent scope. Some people like a Bullet Drop Compensator (BDC) scope but I find them more of a distraction than useful in the field. Before a BDC scope can predict bullet drop, you must know the distance to the target and you must set your scope on the highest magnification because that’s the only magnification where the BDC is calibrated. This is fairly easy to do at a range but not so easy in a prairie dog town or in the woods. Nikon has a better solution with their “Spot On” software. It allows you to use any magnification then assigns a distance to each horizontal line. If you look at the above chart for a 223 Rem you will see distance and hold over can be quite critical …. tight enough where you will miss a “quarter” sized target more than you will hit with a BDC scope.

Rather than go into all the details of scopes, you might want to download my article in the Ruger Forum Library titled “Scope Dope”. This article details how scopes work and will help you select the best scope for your shooting needs.

Three very important issues …. No one single scope can possibly cover all shooting needs. Never buy a scope based on “what ifs”, rather buy it based on “real needs”. No scope can possibly improve accuracy beyond the capability of the rifle and ammo. 16 References:

QuickLOAD ( software) http://www.neconos.com/details3.htm

Ballistic Explorer (external ballistics software): http://www.dexadine.com/bexmain.html

Nikon Spot On software http://spoton.nikonsportoptics.com/spoton/spoton.html#:4

Coriolis Effect information Wikipedia https://en.wikipedia.org/wiki/Coriolis_force

Scope Dope (Ruger Forum Library) http://rugerforum.net/library/61505-scope-dope.html

Mysteries of Smokeless Gunpowder (Ruger Forum Library) http://rugerforum.net/library/29181-mysteries-smokeless-gunpowder.html

Lead Bullets and Revolvers (Ruger Forum Library) http://rugerforum.net/library/19869- lead-bullets-revolvers.html

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