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Rifle Ballistics for beginners

Notes by Donald K. Burleson

January 2011

Long Distance Rifle Ballistics:  A Guide for the Competitive Rifleman

You never get a second change to make a good first shot, and this book is indispensible for any long-distance rifleman who needs to make their first shot count.

This handbook is designed to give the professional and non professional long distance rifleman a functional understanding of ballistics without obtaining a four-year degree in physics.  While much of the content of this book is supported by proven science, we deliberately skip-over the dense math and over-generalize and simplify each concept.  Starting with easy-to-understand elementary rifle ballistics principles we illustrate each concept in plain English and easy to understand illustrations.

Towards the end of the book we fill-in the blanks and create a comprehensive view of rifle ballistics, complete with the equations, and annotated with proven scientific studies.

High on pragmatism and short on theory, this is an indispensible ballistics guide to the big game hunter, competitive marksman and military sniper.

By the end of this book you will have a general appreciation of every aspect of firearms ballistics and understand the relative importance of each factor, all the way from the trigger pull to impacting the target.  The concepts in this book provide insights that make the difference for any competitive long-distance rifle competitor.

This is a must-read book for anybody who needs to understand the physics behind firearms ballistics. If you are already an expert marksman who needs that “competitive edge”, this is the book that can make the difference between success and failure.

 

Introduction

Ever since the Chinese created the first hand-cannons from large stalk of bamboo, people have been working out ways to make firearms functional over longer and longer distances.

Even as late as the American Civil War, cannon ballistics was an inexact science, an expensive trial-and-error process that was both inefficient and dangerous.  Even in 21st century Afghanistan, U. S. military studies show that it takes nearly a quarter million rounds to kill a single terrorist.

It’s important to remember that every gun is unique and that even tiny factors can make a huge different when shooting at distances of 1,000 yards or greater:

Rifle action and body

Every rifle is unique and has its own “signature” for optimal ballistics.

Ammunition

Many professional marksmen used “match grade” ammunition and target shooter will reload their own ammunition.

Trigger

A championship trigger should have a pull of less than five pounds, with limited “travel”.  At trigger release time, the release should be “crisp”, like the feeling of snot on glass.

Barrel wear

Barrels need breaking-in, just like a car.  Also barrels wear out, especially high caliber rifle chambers.  Barrel life is directly influenced by the peak pressure in the barrel (near the chamber) and by gas volume.

Bullets 

Obviously, the shape, size and weight of a bullet make a vast difference in accuracy.  The weight of a bullet is especially important when shooting a living target.  It’s not just the velocity of the bullet that counts; the higher the weight of the bullet, the higher the Kinetic energy.  Higher Kinetic energy increases the gyroscopic stability for long distance shooting (usually shot from a rifle with a faster twist).  A higher Kinetic energy also improved the wallop at impact.  It’s like the different in impact damage after being hit by a golf cart versus being hit by a dump truck.

This chapter will take a brief look at the history of rifle ballistics so that we can appreciate the impact of technology of long-distance shooting and understand that some fundamentals have not changed in centuries.

Basic Ballistics Terminology

Xxx

External factors:

Winds 

A good marksman must be able to gauge “windage”, the side-to-side variances in the bullet flight path caused by the speed and direction of a breeze.  Over distances greater than half a mile there may be multiple winds, each at a different direction and velocity.  Expert riflemen have a sixth-sense that has been dubbed “Kentucky Windage” because it looks like magic.

Gravity 

Normally gravity is a constant, but it the real-world gravity is less at the equator than at the poles!  The earth is not round, it is pear-shaped and widen below the equator.  The centrifugal force measurable reduced the pull of gravity at the equator (the Coriolis effect <ADD CONTENT>) Gravity also plays a role at altitude.  For example, a 55 grain bullet at sea level will weigh less than 55 grains at 14,000 feet of altitude.

Because the rifle path must be arched-upward to account for the pull of gravity, there will always be two spots where a bullet will cross the target elevation.  For example, an AR-15 with “battle sight zero” will  sight at 38 yards and 300 yards.

 

Air Density 

Dense air (barometric pressure) produces more bullet “lift” and also helps by providing a mirage for you to gauge wind direction and speed.  This is why high altitude mountain goat shooting is more challenging than big game hunting at sea level.

Air Temperature 

Hot air is thinner than cold air, and all else being equal, a bullet will travel farther and higher on a cold day.

Movement of the earth

The earth constantly rotates to the East at a speed of 750 miles per hour.  We do not notice this movement as wind because the atmosphere is also rotating at an identical speed, but we do see evidence of this rotation in the “jet stream” at high attitude.  The jet streams snakes eastward in the northern hemisphere in direct reaction to the earth’s natural movement.

Water DOES NOT rotate in different directions at each side of the equator.

The Coriolis Effect is too small to measure in most cases, but long-distance projectiles must consider that the earth is moving beneath them.  In most cases, only huge artillery (8 inch bore or greater) considered the movement of the earth.

 

Relative motion

Assume that we have a bullet fired backwards from a jet fighter travelling at 2,000 miles per hour with a muzzle velocity of 2,700 feet per second (1,841 miles per hour).  The bullet would still maintain its speed through the air even though the “real” speed of the bullet upon hitting a stationary object would be negated by the elative motion.

Conversely, firing a bullet forward from a fighter plane moving

would be

 

Bullshit? (page 106)

British Small Arms committee in 1886 said that the movement of the earth  causes a 6 inch deviation at 1,000 yards in the Northern hemisphere and a corresponding six inch left deviation in the southern hemisphere.

Maximum drift occurs when the bullet is fired toward the Southeast and the minimum drift occurs when the bullet is fired toward the northwest.

The amount of deviation due to the earth’s rotation is varies according to the distance from the equator.

“Generally, the bullets curve will be about one tenth of an inch in 125 yards in the central part if the US”. (Ricker, p106)

 

Hollow-point bullets have the negative consequence of shifting backwards of the center of gravity but they also improve gyroscopic stability by decreasing the de-rotation effect.

 

Precession pg 90

 

 

Nutation (page 93)

 

 

Type of ballistics

·         Internal ballistics:  These are the machinations that occur between the chamber and the end of the muzzle.  These internal ballistics are hidden and hence, very difficult to measure empirically.

·         External ballistics: External ballistics covers the distance from the muzzle to impact and includes the flight path and aerodynamic characteristics of the bullet.

·         Forensic ballistics:  The term” forensics” relates to a study of the law, and forensic ballistics is used by law enforcement to measure the

 

All rifles from a .22 caliber plinker to a 50 caliber sniper rifle operate on exactly the same principles of ballistics.  Let’s start with a simple review of the parts of a rifle:

·         Trigger

·         Chamber

·         Barrel: The barrel is an extension of the bullet chamber that holds the gasses as they burn.  The barrel is exposed to tremendous pressure such that only metal is strong enough to contain the pressure.

·         Muzzle:  This is the exit point where the bullet and gunpowder meet the open air.  There are several attachments that may be added to the end of a muzzle including a silencer, a flash suppressor and a muzzle break.

·         Muzzle Brake:  The muzzle brake acts to deflect the upward pressure of the bullet, reducing recoil and keeping the bullet at a flatter trajectory.

·         Rifling:  These are the “grooves” that are cut into the barrel to impact spin.  This spin acts like a spinning top to give the bullet gyroscopic stability.

·         Flash Suppressor:

·         Gas valve:

 

Gyroscopic drift:  about 13 inches for a 30-06 at 1,000 yards.

 

We also need to cover the basic properties of ammunition:

Barrel Caliber 

This is the measure of the diameter of a bullet and barrel interior diameter, measured in 1/100th of an inch.  A .50 caliber bullet is one-half inch wide, and a .38 caliber bullet is about 1/3 of an inch wide.

Bullet

The weight of a bullet is measured in “grains” with 7,000 grains per pound.  Table 1.1 shows the common weights associated with common calibers of bullets.

Shell casing

The Brass quality influences the bullet trajectory.  Some shell casing the not completely round, but slightly conical shaped, wider at the primer-end and tapered by a few thousandths of an inch where the bullet is seated.  Consider the difference between a .22 magnum cartridge and a standard .223 cartridge (Figure x.x).  These buckets are essentially the same caliber, but the .223 bullet is 55 grains and the “shoulder” in the shell casing allows a much greater diameter of powder in the chamber (Figure x.x).

This idea of having a cartridge that is of a larger diameter that the caliber allows for increased pressure for the bullet, but the slant of the shoulder is very important.

I short taper in the shoulder is ideal for increasing bore life, while a longer taper will cut-down on the bore life because of the way that the expansion of the gunpowder forces the brass into the front of the chamber.  In competition rifles with fully-packed cartridges (e.g. 308 at 1,000 yards) the forces in the chamber causes the barrel chamber to become sub-optimal after only 1,100 rounds. (Figure (x.x):

 

 

 

Bullet Crimp: 

A tighter crimp of the bullet to the shell means that more internal pressure is required to start the bullet moving down the barrel.

Powder

The gunpowder is a mixture of chemical that can burn at a very fast rate without the benefit of oxygen.

Primer

A primer is an unstable chemical such as “fulminate of mercury” that create a fiery “flash” when struck by the trigger firing pin.

Other Terms:

·         Muzzle Flash:  This is where un-ignited gunpowder residue meets with oxygen and buns.  A muzzle flash is impressive, but it gives-away a snipers position, and from a ballistics viewpoint, a muzzle flash indicates wasted energy.

·         Muzzle Velocity:  This is the speed (measured in feet per second (fps)) for a bullet as it leaves the muzzle.  The muzzle velocity can range from 100,000 feet per second (about 682 MPH) for a small .22 caliber plinker to over 3,000 fps (2,000 MPH) for a .50 caliber sniper rifle.  The muzzle velocity varies inversely with the mass of the bullet (small mass = higher velocity), and the muzzle velocity varies directly with the size of the caliber (greater caliber - greater velocity)

Barrel

A barrel must be both strong and flexible, and only metal compound have the strength to hold the high pressure of the gunpowder reaction and the flexibility to deal with the forces made by the bullet.  All else being equal, a fat “bull barrel” is better at minimizing barrel movement, but the extra weight makes it hard for soldiers.

Today, barrels are made from titanium and stainless steel and no plastics or non-metal compounds can contain the pressure of a gunpowder charge.

 

 

 

Gunpowder Ballistics

Contrary to popular opinion, gunpowder does not explode, it simple burns quickly.  While a firecracker is essentially black powder wrapped into a tight paper tube, gunpowder burns at a fast rate but it does not explode.

To understand this, let’s look at the relative burn rates for C4 explosive vs. modern gunpowder:

xxx

Original black powder date back to the Middles Ages and was created with simple ingredients:

·         Charcoal:  This is the “fuel” for the burn. (15%)

·         Saltpeter:  Salt peter is created by spreading line over animal feces and harvesting the drainage, creating Potassium Nitrate (KNO3). (75%)

·         Sulfur:  This is the only “mined” component of black powder. (10%)

In an ideal world, black powder gunpowder would burn as a constant rate, but in reality, gunpowder burn rates are influenced by are within the chamber (“squib” loads), moisture (“Keep your powder dry”) and many other factors.

Pressure is also required for the chemical reaction in gunpowder.  At the pressure peak (one inch or so from the chamber, the pressure can exceed 50,000 pounds per square inch (psi) while the pressure at the muzzle exist drops to about 5,000 psi. (Figure x.x)

 

Figure x.x – Changes in pressure for a travelling bullet

 

At the mid 19th century black powder started to be replaced by “smokeless powder” a different chemical cocktail with different burning properties. Smokeless powder was called “plastic monopropellant” and it was very advantageous because it was less messy and corrosive and allowed a shorter barrel, making for easier combat with lighter rifles.

Alfred Nobel (of Nobel Prize fame) helped develop modern gunpowder’s and it’s interesting that the ”fuel” for the gunpowder chemical reaction was changed from charcoal to cellulose fibers, originally carbohydrates or cotton fibers.  The smokeless powders also allowed manufacturers to create coated particles with more uniform burn rates.

Today we see “fast powders” that burn to create higher bullet velocities used in shotguns and pistols, while we see “slow powders” that are used in long distance rifles.

 

 

 

 

 

 

 

·         Shotguns use a dense “heavy” powder

·         Handguns require a “fast-burning powder”

·         Long distance rifles use slow-burning powder:  All else being equal, a slower gunpowder requires a longer barrel.

 

 

Modern gunpowder is very stable and will only ignite at temperatures in excess of 300 degrees.  100 pounds of gunpowder has the same explosive energy as only 10 pounds ( xx gallons) of gasoline.  When machine gun barrels get hot from excessive firing (e.g. combat) the barrel temperatures can cause the barrel to glow red-hot, causing bullets to “cook off” and ignite spontaneously.

In general, standard ammunition has a ratio of one grain of gunpowder for every three grains of bullet weight.  For example, a 60 grain bullet would require approximately 20 grains of gunpowder.

It is not necessary to completely fill the shell casing to the bullet, and you can create lighter loads called “squib loads”.  Squib loads can be used for practicing and help with barrel longevity in large caliber target rifles.  When using Squib loads it’s important to pack the powder down at the primer-end using an inert substance such as Dacron or Kapok.  A 15% decrease in the volume of the gunpowder will reduce stress at pack pressure (immediately outside of the chamber) and translate into a 25% increase in barrel life.

 

 

Firing Ballistics

At firing time, the following sequential steps occur:

Trigger time

Ignition time: Internal combustion

As the gunpowder burns there is a rapid increase in volume, but this pressure is not uniform.  Initially, the pressure builds to a point where the bullet begins to travel from the shell casing, but in less than a quarter inch, the pressure drops off.  This drop is pressure is a function of the bullet acceleration and the energy required to start the spinning through the rifled groves of the barrel.  By the time the barrel leaves the barrel the bullet can spinning at over 250,000 RPM and travelling at over 1,000 feet per second.

Only 30% of the gunpowder energy goes to the bullet.  Another 30% is wasted as heat energy and 40% is wasted on noise and recoil.

Greasing a bullet shell can cause less space in the chamber and cause the brass to slide forward into the chamber causing a 30% increase in chamber pressure. In general, it’s not a good idea to polish or grease a chamber as some friction is required to properly seat the shell casing.

Recoil begins while the bullet is still in the barrel.

If you disable the gas valve in a semi-automatic rifle, the recoil increases but the muzzle velocity will decrease by 15%.  (page 69)

Pistol Caliber     Bullet    Charge                  muzzle velocity

.22                            40         01.1                        800 fps

.32 auto                  50         00.9                        760 fps

.38                            88         03.8                        990 fps

.357 mag              158         16.0                        1,235 fps

.45 Colt                 250         08.5                        860 fps

 

Rifle Caliber       Bullet    Charge                  muzzle velocity

.223                            55       27                          3,240 fps

.308                          150       47                          2,820 fps

.3030                       170       32                          2,200 fps

 

 

Bullet Ballistics

A bullet shrinks in diameter as it moves down the barrel. 

Studies have shown proven that this bullet shrinkage is related to barrel length:

A) A bullet is fired into water and the bullet retrieved and measured with a micrometer.

B) One inch is cut-off from the muzzle end of the barrel and the test is repeated

In each successive trial, the lossage in caliber decreases

 

Chapter x:  Barrel Ballistics

The pressure of the bullet moving through a rifled barrel creates centrifugal force.  Even in a rifle with a slow twist, exist spinning can exceed 250,000 RPM, placing a huge outward force on the bullet.

A new barrel needs to be “broken in”, using a method called fire-lapping.  For competition high-powered rifle barrels, a complete log of every round fired is required and barrels are replaced every 1,100 rounds.  When a barrel is replaced, it is because the chamber-end has become sub-optimal (CARL WHY?)

A used barrel can be removed and a new chamber drilled, making a useful barrel that is several inches smaller than the original barrel. 

The length of the barrel influences the exit pressure (muzzle velocity).  This data for a 30-06:

Barrel Length     Muzzle Velocity

24 inches             2,700 fps

30 inches             2,850 fps

There are limits to effective barrel length.

A .22 rifle is most efficient at a 18” to 22” barrel length.

 

 

Barrel whip and bulge

As the bullet moves through the barrel, a “whip” effect is imparted.  It’s like holding a fishing rid horizontal and quickly flipping it upward.  The end of the fishing rid quickly moved downward and then reacts and begins moving upwards.  As the bullet moves through the barrel, a bulge is formed immediately before the bullet.  This “swelling” move down the barrel ahead of the bullet and the expanding gasses, ending with the bullet traveling slightly upwards as it exist the muzzle.

 

The rifling also imparts torque on the barrel, in the opposite direction as the rifling.  A 30-06 will show as two inches left (from a right-hand rifling twist) at 500 yards.

As the bullet leaves the muzzle, this centrifugal spin can cause the bullet to “yaw”, creating a spiral helix pattern.  Anyone familiar with the “double helix” of DNA knows the look of a spiraling bullet flight path.

In long distance rifles, this spiraled flight path is quite small, not exceeding the diameter of the bullet.  In some long range bullets it takes 200 yards for the bullet to become completely stabilized.

Free Boring

The idea of free boring was to leave an un-grooved area for a few inches past the chamber with no rifling.  This was supposed to give the bullet a “head start” down the barrel before the rifling kicked-in to impart a spin.  Free boring does not work

For the best accuracy, the rifling should meet the chamber, and the bullet actually touching the rifling at trigger time.

Gain twist

A Gain twist happens when the rate of twist increases toward the muzzle end, increasing the acceleration of the bullet spin at the end of the rifling.

Measuring rifling twist

It’s easy to measure rifle twist.  All you need is a standard brass cleaning rod, a “sharpie” marker and a measuring stick.

1 - If possible, clamp-down the gun to remove movement.

2 – Thread a cleaning rag through to open hole in the flat side of the rod plunger.

 3 – With a sharpie, draw a line down the length of the brass cleaning rod.

4 - As you start the plunge, mark the barrel at the point where the rag begins to twist into the grooves of the rifling.

5 – As you continue to plunge the rode down the barrel, you will observe the brass rod twisting as it progress.  When the rod reaches the point of a full-twist (as denoted from your first mark on the barrel), make another “cross mark” on the rod and withdraw it.

5 – Now, simply measure the distance between the end of the rod to your cross mark.

This distance will be the travel for a single rotation.  If the length is 7 inches, you have a 1:7 twist.  If you have 12 inches, you have a 1:12 twist.

 

Optimal rifle twist

It is a common misconception that it is the weight of a bullet determines the optimal gyroscopic twist rate twist rate.  The gyroscopic stability varies as the square of the rifling twist, such that a small change in twist creates a big change.  This is because the velocity is a function of the square of the rotational speed, such that a small increase in rotational speed results in a large decrease in velocity.

 

The Greenhill equation is named after Alfred Greenhill, a ballistics researcher in the late 1800’s.  He developed a fairly accurate equation for estimating the “optimal” twist for a barrel based on the bullet length and the caliber.  The Greenhill equation uses a constant of 150 for muzzle velocities under 2,000 feet per second and 180 for muzzle velocities greater than 2,000 fps.

Greenhill says that it’s the LENGTH of the bullet that matters, not the WEIGHT (even thought the length and weight are correlated).  Important note:  A linger bullet requires more gyroscopic stability (a faster spin).  Hence, a longer bullet is more susceptible to a “tumble” at long distances than a short bullet od equal weight.

A pointed bullet has more aerodynamic stability than a round-nosed bullet but it has an increased risk of tumble.  A U. S. Army study in 1880 using .45 caliber round nose rifle bullets (500 grains) at 3,500 yards (almost two miles) showed that the fat round tip bullets did not tumble at great distances.  At 3,500 feet, the bullet was exhausted and had an impact angle to the ground of 65 degrees, but the bullet was still tip-forward!

All else being equal, pointed tip bullets will tumble at this distance.

Given:

30 caliber bullet = .308 inches in diameter

Bullet length (inches) = 1.125

Optimal Twist = (150 / (Bullet Length/Caliber))*Caliber

= (150 / (1.125/.308))*.308

= (150 / 3.65)* .308

= 41.09 * .308

= 12.65 twist

If two bullets have the same spin and speed, a longer, heavier bullet will keep gyroscopic rotation better then a short, light bullet.

If you control velocity with handloading, you can stabilize a bullet coming from a slower twist barrel.

 

Too much twist

“Because of tumbling”, some experts say that when the M-16 rifle barrel twist was change from 12 to 14, the killing power was reduced” – (Rinker, p 145)

The 30’06 used to have a 10 twist, perfect for heavy long bullets (over 125 grains), but that was changed to 12 or 14 to accommodate lighter bullets.

Switching to a longer or heavier bullet require a faster twist, resulting in less accuracy at long distances.

 

Effect of specific gravity of the bullet

Weight of dry bullet minus weight of bullet submerged in water.

 

 

 

The .22 short (with 30 grain bullet) always performs best with a 1:20 inch twist

The .22 Long Rifle (with a 40 grain bullet) always perform best with a 1:16 inch twist

 

 

Barrels and Ballistics

Initial drilling is .01 inches larger and final reaming takes down the barrel to the caliber size.  Periodic heat-treating during manufacture relieves metal stress and makes a target barrel more accurate.

Testing by Eric Johnson of Hoffman Arms Vo. showed that the optimal velocity was a function of barrel length and the “best” barrel length for a 22 LR bullet was only 18 inches. (Rinker, p118).

The wide “Bull barrel” style is fat all the way from the chamber to the muzzle, where some target barrels are even fatter at the chamber-end.

 

Bullet design

Ever since the American Civil War, soldiers are vary of the “splatter effect” of the 50 caliber lead mineballs, bullets that left massive wounds.  (figure x.x)

 

Figure x.x:  A lead mineball

 

The hippies in Europe decided that the world needed “clean kill” bullets and many people mistake that the Geneva Convention created the idea of the “steeljacket” bullet, a soldiers bullet with less expansion upon impact.  In reality, it was the Hague convention that mandated the use of steeljackets and America refused to sign this declaration.

However, ballistics studies have shown that steel jackets have enhanced flight properties and today’s bullet jackets are not uniform.  They are thickest at the base and back side, and the jacket wall tapers towards the point (see Rinker, p 210)

 

Most of today’s bullets go supersonic before they exist the barrel, expect for some small .222 caliber sub-sonic bullets.  The effect of air drag are very important to a supersonic projectile, whether it is a jet fighter of a sniper bullet, a pointed head helps reduce drag and increase gyroscopic stability.

The boat tail bullet base

The study of supersonic rifle bullets led to the implementation of the “boat tail” base (a.k.a. a “tapered heel”) as seen in Figure x x.

 

Figure x.x:  A regular and a boat tail bullet

The boat tail bullet can reduce air drag by as much as 20%.  This is only helpful for supersonic bullets with long-range shooting (at least 200 yards).  For example, a small caliber supersonic bullet at 200 yards will have a very short flight time, and a 20% air drag reduction would not have a statistically significant effect on the impact velocity of the bullet.

The boat tail design has several competing characteristics:

·         Positive:  The boat tail taper helps reduce the partial vacuum that exists behind the bullet.  The boat tail also reduces the deflection from crosswinds, especially at ranges of 1,000 yards or greater.

·         Negative: During supersonic flight a ripple effect can be seen, and this shockwave can impede accuracy.

The optimal compromise between these competing effects is a boat tail taper diameter of .4 inches of the caliber (or less).  (Figure x.x) (Rinker p 205)

·         A .308 bullet might have a boat tail of (.308 * .6) = 18 caliber diameter at the base of the boat tail.

·         A .50 caliber bullet might have a boat tail of (.5 * .6) or about 30 caliber.

At distances of 1,000 yards or greater a boat tail bullet is mandatory for accuracy, and the boat tail reduces wind deflection such that a 10 MPH cross wind will cut the bullet deflection by three to four feet (Rinker p 204).

Bullet ogive design

The “ogive” of a bullet is the shape of the nose of the bullet, expressed as the straight line originating from the curvature of a circle (Figure x x):  The ogive is expressed as the radius of the line that intersects the imaginary center of the circle.  Note that bullets are never purely conical-shaped, and the ogive only measure the straight-line taper of the nose of the bullet.  The ogive length is equal to the caliber of the bullet multiplied by half of the square root of the quantity 4*(caliber_radius)-1.

The meplat

Competition rifle bullets never have a completely sharp nose because if issues with semi-automatic guns.  Instead, a small flat spot exists at the most called the “meplat”, a flat surface

What is a “spitzer” shape?

 

Bullet characteristics

All else being equal:

Expert competition shooter will always hand-load their cartridges.  No factory ammunition can match the care required to make multiple bullets with the exact same loads and precision.

Lighter bullets create faster muzzled velocities and flatter trajectories.

Heavy bullets have a lower muzzle velocity but they are more stable and have greater impact momentum.  Heavy bullets must also be carefully matched to the barrel twist, and heavy bullet requires a faster twist.  For example, many competition shooters of .223 rifles with use a 1:7 twist, and use heavier bullets.  Using a heavy bullet with the “standard” 1:9 twist in a .223 would cause the heavy bullet to lose gyroscopic stability at long distances and tumble, creating a “key hole” shaped impact hole.

Blunt-nosed bullets are not appropriate for distances greater than 200 yards and blunt noses are more susceptible to wind drift than pointed nose bullets.

 

 

 

 

 

 

 

 

 

 

The insanity of “illegal” bullets

By great Grandpa Jonathan Hardister was shot by a “mine ball” at the battle of Gettysburg and it tore a massive hole in his side.  It took him years to recover from a wound that would not have been life-threatening if it had been a “jacketed” bullet that did not expand or splatter on impact.

The “humane” steeljackets

The Geneva Convention came up with the idea of the steel-=jacketed bullet for humane reasons, a reason to have a clean kill and less agony for near misses.  In concept, the steeljacket is fine when you are up against an honorable enemy as in WWII where the Japanese and Germans adhered to the steel-cased bullets.

But today we deal with a morally-corrupt and Godless enemy who has no problem using their own women and children for suicide killings.

American soldiers need an equalizer, and it’s sad that we must lose the lives of our young people to adhere to a higher moral standard than the dastardly terrorists. 

My nephew is a master sergeant in the Marines who teaches close-up defense, and by the time a Marine needs to pull their sidearm, they are in dire straights; being overwhelmed by the enemy at close range.  The military has traded the higher stopping power of the .45 caliber semi-automatic 1911 pistol for the higher capacity of the Beretta and ??? 9mm bullets.  The 1911 holds (x + 1) while the 9mm holds xx + 1 bullets).

It’s important to note that using hollowpoints and exploding bullets are not intended for machinery and thick-skinned big game.  These technologies are designed or thin-skinned prey (deer and terrorists), and the hollowpoints do not have the penetrating power for karee game with thick hides..

Hollow Points

Creating a hollow point in any handgun bullet has a negligible effect upon the ballistics and increase the propensity of the bullet to expand upon impact.

Mushrooming

The term “mushrooming” refers to the curling-back of the point of the bullet upon impact forming a mushroom-shaped appearance (Figure x.x).  Mushrooming is allowed (and encouraged) for personal defense and law enforcement loads.  Today, civilian ammunition allows for “moderate” killing power in home defense loads.  For example, the Hornady home defense loads have a hollow point filled with a plastic tip that allows for expansion and “mushrooming” of the bullet upon impact (Figure x.x).  The law allows for moderate mushrooming, but not as far as the technology will allow.

·         Radioactive bullets:  In the military, the 50 caliber anti-tank bullets use heavy metal nuclear waster uranium ??? to allow the bullet to penetrate the heavy steel case of the tank and then explode. (Figure x.x).

However, there have been deliberate limits placed upon the killing power of handgun bullets.

 

Illegal loads

I believe that American soldiers and law enforcement should have access to special handgun shells that have explosive power on impact.  There have been several cases of posthumous Medal of Honor recipients (get names) where the soldier died in panic being killed by an overwhelming force.  It does not have to be this way.  We have the technology to create a pistol bullet that explodes on impact and will cut a terrorist in half, stopping them immediately.  Our soldiers deserve this “edge”;

Ever since Henry Shrapnel discovered that a bomb could be placed inside a cannonball, ballistics experts have known that a small explosive charge can be placed within a projectile (Figure x.x):

 

Henry Shrapnel and the exploding projectile

Henry Shrapnel’s legacy is easily miniaturized and can be used in medium and large caliber handgun bullets.  Some illegal concepts include:

·         Steel balls in hollow points: You can place a hardened steel bearing inside the cavity of a lead hollow-point bullet causing the ball to be thrust backwards at impact, causing the bullet to greatly increase in diameter (mushrooming) (site book).

·         Mercury in hollow points:  Mercury embedded inside the nose of a bullet will create an explosive effect upon impact.

·         Disintegrating bullets:  Some brittle metals have the properties if fragmenting upon impact, leaving hundreds if tiny shards in the prey.

Allowing these “illegal” technologies for law enforcement and the military would negate the effect of switching from the lower capacity 1911 .34 semi-automatics to the higher capacity 9mm handguns because an exploding 9mm round would have the take-down power to stop a bad guy in their tracks.

The speed of sound

Every child is taught to estimate the speed of sound when estimating the distance between seeing a lightening flash and hearing the crack of the lightening.  Counting “one-thousand-one, one-thousand-two) gets the number of seconds, and multiplying by 1,130 gives the distance in feet.  For example, if it is 5 seconds between seeing a lightening flash and hearing the crack, you know that the lightening hit about a mile away. 

In combat ballistics, the same principle applies.  If you see a sniper bullet crack a tree branch in front of you, and you hear the rifle crack 1 second later, you can estimate the distance by estimating the average velocity of the incoming bullet.

The speed of sound is important for long distance rifle shooting because of the unique aerodynamic turbulence that occurs between Mach .9 and Mach 1.1.  A rifle bullet goes supersonic while still in the barrel and the “crack” of the bullet exceeding the sound barrier can be heard in the forum of a 70 degree cone emanating from the end of the muzzle (Figure x)

 

Figure x x:  The cone of hearing a bullet exceed the speed of sound

Note that this is the reason why you cannot use a silencer with a high powered rifle.  The silencer cannot control the sound waves that are created inside the barrel when the bullet goes supersonic.  It’s all Hollywood, like putting a silencer on a revolver, not knowing that the space between the cylinder and the barrel emits a huge sound!

Avoiding the instability of this “transonic” mode is very important, especially at long distances when a bullet degrades beck to subsonic.  At trigger time, the newly-supersonic bullet many be unstable for up to 200 yards until it shakes off the turbulence of the sound barrier, but these shakes will reoccur when the bullet degrades below 1,300 feet per second downrange and the shockwaves reoccur.

Avoiding the trans-sonic range is why many .22 competition bullets are deliberately subsonic because the momentum is offset of the turbulence.

Hence, the impact velocity should always be supersonic if possible, keeping at least 1,130 feet per second.  The denigration into the trans-sonic range causes huge air drag and possible loss of gyroscopic stability and bullet tumbling end-over-end.

Velocity

The maximum velocity with conventional powders if 6,500 feet per second, with 4,500 fps as a practical maximum velocity.  In a nutshell, a bullet can never move faster than the expansion rate of the propellant (Rinker, p 167)  (look up “wildcat” cartridges.)

Sectional Density

A higher sectional density (high weight) gives a flatter trajectory.  A lower sectional density has a greater velocity loss, a higher trajectory arch.  A heavy bullet is also less susceptible to wind.  On impact, a heavier bullet will have more penetration.

 

 

 

 

 

 

 

 

 

 

 

 

The speed of sound is not a constant; it varies according to several factors all related to the density of the air.  These factors are listed in order of importance):

·         Attitude:  The speed of sound slows slightly at greater altitude.

·         Temperature: The speed of sound slows slightly at hot temperatures.

·         Humidity The speed of sound slows slightly at in dense air.

Note that this difference is too small to be of much importance.  For example, at 10,000 altitude shooting a target at 300 yards, only a 1/2 MOA downward adjustment would be required. (Rinker, p 157)

Velocity

All else being equal, the temperature affects the velocity of a bullet.  For example, a 30 degree drop in temperature will cause a corresponding loss of over 50 feet per second.

 

Air pressure and air drag

The air pressure at sea level is 14.7 pounds per square inch and this varies according to barometric pressure.

The air drag over a bullet is called “”skin friction” or “parasitic” drag” and air drag is on of the most important factors in the flight of a bullet.

For example, consider a 30’06 bullet fired straight up.  The bullet starts at 2,700 feet per second and it will slow rapidly until it reaches its peak altitude at only 10,000 feet before it briefly stops and begins its fall back to earth.  In a vacuum without air drag and only gravity to slow-down the bullet, a 30’06 would travel straight-up to over 100,000 feet before dropping.

It’s counter-intuitive that gravity is far more important that air drag. In the real-world, air drag is 90% more important than air drag.  Interestingly, that same bullet falling from 10,000 feet would quickly reach its terminal velocity of about 400 feet per seconds, again, due to the air resistance.  As the bullet approaches sea level where the air is denser and the terminal velocity becomes slower.

Remember, the vertical pull of gravity is not as important you might think.  In The American Rifleman (Dec 1982) author William Davis noted that the difference between dropping a 30’06 bullet from a high of five feet was almost the same!  The shot bullet travelled 1,310 feet downrange, yet it only hit the ground a half second faster than the un-shot bullet that was dropped from five feet!

1 A 30 caliber M72 match bullet will travel 1,000 yards in 1.66 seconds

Terminology

Dram:  A dram is a unit if weight equal to 27 grains

Slug:  A unit of mass

 

References:

Kelley & Reno, Exterior Ballistics, by McShane, 1953

Lowry, E. D., Exterior Ballistics of Small Arms Projectiles, Winchester Western Division

Rinker, Robert, Understanding Firearms Ballistics, Mulberry House Publishing, 1998

 

Range & Ballistics tables

RE-start at Chapter 17

 

 

 

 

 

Note: The opinions expressed on these pages are the sole opinion of Donald K. Burleson and do not reflect the opinions of Burleson Enterprises Inc. or any of its subsidiaries.

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Copyright ? 1996 -  2010 by Donald K Burleson. All rights reserved.