There is a lot of misinformation surrounding firearms industry, usually coming from a gun dealer or a helpful but misinformed friend or family member. This article explains some of the concepts of terminal ballistics and how they apply to handgun self defense.

Terminal ballistics is the study of the effect of a bullet on the target, in the case of self defense this is often another human or small animal such as a dog.

A knowledge of terminal ballistics will help you identify what information is correct, and what is biased or wrong.

There is a great deal of information available on the Internet about terminal ballistics on humans and some of the best can be found in a report the FBI released called “Handgun Wounding Factors and Effectiveness” which is an in depth discussion of terminal ballistics on humans.

This subject is highly complicated and large amounts of information have been created on it. It is my goal to give you a primer without overwhelming you.

Bullet construction, weight, shot placement, physical construction and the mental makeup of the bad guy all play huge parts in how many shots and how long it will take to stop him or her (some people pass out when shot, others can stay in control for long periods of time).

#1 Penetration and shot placement are king

Handguns stop a bad guy by penetrating his vital organs, if your bullet is incapable of reaching those organs no matter how well placed the shot it may not be effective. Shot placement is important because a bullet that is able to penetrate is not effective if not placed in vital organs.

Penetration

The FBI determined the ideal penetration range 18 inches with a minimum of 12 inches of penetration. People often worry about over penetration and make the statement that 18 inches is excessive, this is incorrect for several reasons:

#1 A handgun stops a threat by penetration, the temporary wound channel is not effective for handguns because the bullet is moving too slowly, without penetration a gun is ineffective.

#2 You may not have a perfect shot, while few humans are thicker than 12 inches from the chest to the back, a shot from the right side through requires more penetration, shooting through barriers such as a coat, or arm also increases the required penetration

#3 You don’t want the bullet to reach the vitals, you want it to destroy them, as a bullet slows it begins pushing tissue aside rather than causing damage, you want enough energy left to cause damage once the vitals are reached.

#4 America is getting bigger, recently the medical field increased the length of needles, the coast guard has had to recalculate capacity ratings of boats, all because Americans are getting bigger. The larger a person is there more fat and muscle the bullet must penetrate before reaching vitals.

Shot Placement

Shot placement means putting the bullet in an effective area, while many people advocate shot placement as the single most important factor I disagree and view penetration as slightly more important. Proper shot placement is insignficant if the bullet is unable to penetrate to vitals, likewise a bullet is not effective if it doesn’t pass through vital organs.

There are three shot placement areas:

Electrical: This is shooting the head, this is highly effective because it instantly disrupts the electrical system of the body, unfortunately head shots are extremely hard to deliver because the head moves from side to side and is a fairly small target. For self defense the head shot should rarely be the initial target.

Center of Mass (COM): This is the heart and lung area of the chest and is the primary shot placement area, it is a large area and doesn’t move much. COM should be the standard default target, COM hits work by causing the lungs and heart to stop working, this means the bad guy can have up to 15-30 seconds of willful control to do you harm. If COM hits are ineffective they can be followed with an electrical shot (see above).

Structural: These are hits to the frame of the body, for example to the arms or legs and are very ineffective at stopping a bad guy. A bad guy hit in a structural area may stop the attack, but if he does it is leisure. The goal of self defense should be to force the bad guy to stop his attack, not ask him to.

#2 Expansion can be a valuable aid

There are two primary types of bullets for handguns, Jacketed Hollow Point (JHP) and Full Metal Jacket (FMJ).

Jacketed Hollow Point bullets can dramatically increase the effectiveness of handgun bullets on humans, these bullets begin expanding once they hit the target, increasing the odds of doing damage to a vital organ, and also reducing the chances of the bullet passing through the target and injuring others. JHP bullets are extensively used by police departments both because of the increased effectiveness and to reduce shooting through the bad guy.

JHP bullets are particularly good for smaller calibers such a 9mm bullet is .355 inches in diameter, with 50% expansion the bullet is now .532 inches or slightly larger than a non expanded 45 ACP bullet (.451 inches).

The trade off for expansion is the larger bullet looses momentum more quickly and doesn’t penetrate as much, thus in very small calibers such as the .380 ACP FMJ may be a better choice.

Full Metal Jacket bullets do not expand when they hit the target and are used by the military (which are prohibited from using expanding bullets) and for target practice. Because FMJ do not expand they penetrate excessively and are not suitable for most self defense scenarios where the target is likely to be a human.

FMJ is a good choice for woods carry because the muscle of cats, wolves and bears can cause JHP to expand and not penetrate enough to stop the animal.

Energy, Velocity , Momentum and Sectional Density

There are several factors to consider when estimating ammunition performance, they are energy, velocity and momentum, energy and velocity are often printed on the box, unfortunately a more significant value momentum is not, luckily both energy and momentum are easy to calculate.

Energy: Measured in ft/lbs this is the kinetic energy of a bullet or how hard it hits, this number is often promoted heavily on ammunition boxes. You can calculate energy by: Energy = ((Bullet Weight * Bullet Weight) * Velocity) / 450400.

Momentum: Momentum is a product of velocity and the mass of an object, the more momentum something has the harder it is to stop it, this is why it is harder to stop a semi truck than a passenger car. You can calculate momentum by doing: (Bullet Weight / 7000) * velocity

Because momentum is a factor of both velocity AND mass this means that a heavier bullet, though traveling slower may have higher momentum and thus perform better.

Sectional Density (SD): Sectional density is essentially the bullet size to weight ratio. Bullet weight alone is not enough to calculate performance, you must also take into consideration the width of the bullet. A 180 grain bullet with a width of .401 has a higher width / weight ratio than a 180 grain bullet of .451. You can calculate sectional density by: ((Weight / 7000) / (Diameter * Diameter)

Velocity: Measured in feet-per-second (fps) this is how fast the bullet is traveling. The same ammunition will develop different velocities in different guns so the velocity printed on the box is only an estimate, in reality it is often less. You can measure the velocity of a bullet by shooting it over a Chronograph.

Estimating Ammunition Performance

There are several things that affect ammunition performance, velocity, momentum, and bullet construction are a few of the big ones. All bullets are not constructed equal, some brands of bullets with the same velocity and weight will perform different, expanding more or less, with more or less penetration. This section details how to compare the theoretical performance of bullets of similar velocity and construction on paper.

The Fallacy of relying on Velocity and Energy

When comparing ammunition in the store often only velocity and energy are available with numbers such as 1195 fps and 491 ft/lb of energy. The problem with these numbers is that by themselves they are not reliable indicators of performance.

One would think 491 ft/lb of energy would be enough to throw a person to the ground when shot, unfortunately this isn’t true and that is because for every action there is an equal and opposite reaction. Were the bullet able to throw the target to the ground the recoil would also throw you to the ground, and clearly most handguns are far from capable of that.

Velocity is also a poor thing to consider by itself, the 40 S&W is capable of pushing a 130 grain bullet to 1300 fps, unfortunately such a light bullet is unlikely to perform well.

What is the answer then? Two things, momentum and sectional density.

Consider the following 40 S&W loads (40 S&W bullet diameter is .401)

40 S&W 135 grain bullet at 1300 FPS

Energy: 506 ft/lbs
Momentum: 25.07
SD: .119

40 S&W 155 grain bullet at 1175 FPS

Energy: 475 ft/lbs
Momentum: 26.01
SD: .137

40 S&W 180 grain bullet at 1000 FPS

Energy: 399 ft/lbs
Momentum: 25.71
SD: .159

If you considered just the information printed on the box (the velocity and the energy) the 135 grain seems to be the clear winner, it is traveling faster with more energy than the other two loads, but once you calculate momentum and sectional density a different picture is painted.

Both the 155 and 180 grain loads have more momentum than the 135 grain load, and both have a higher sectional density meaning they should penetrate deeper and yield a better result.

Because sectional density is constant whereas momentum factors both mass and velocity I give it a higher weight than sectional density when evaluating loads.

Conclusion:

Every caliber has a sweet spot bullet weight with maximum momentum and energy, by using the principles in this article you can find that sweet spot In the case of 40 S&W it is usually 155 to 165 grains, after which momentum drops because velocity drops faster than the increased mass can make up for.

This entry was posted on Wednesday, January 16th, 2008 at 9:06 pm and is filed under Firearms. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.