The Empty-Cases’ Dummy’s Guide to Ballistics

Ballistics – internal, external, and terminal – is a very misunderstood subject. I’ve been studying ballistics since before I killed my first deer. I understand the subject much better than I did then, but I’m still no ballistician. But I am an hillbilly, and hillbillies like to keep things simple.

In almost every gun or hunting magazine we’ll see some reference to ballistics, and the writer very often uses that reference to substantiate some point they’re trying to make. They might be trying to convince you a 45 is better than a 9, that a 300 Win. Mag. is better than a 308, or that you should not shoot a deer with a 223.

When it comes to ballistics, what matters?

And, what do all the numbers and acronyms mean?

Well, if you’ve been desperately seeking those answers, here’s the Empty Cases’ Dummy’s Guide to Ballistics.

Velocity

This is the speed of the bullet. It is the single most important factor when it comes to ballistics because a bullet without velocity is one thing and one thing only: in need of velocity. Velocity dictates trajectory and is the driving force behind expansion and penetration. Lay a bullet in the palm of your hand. Watch it rest there. It is doing all the damage to you it can without velocity.

Energy

Expressed in foot-pounds, energy is supposed to represent how much power a bullet has. Problem is, without terminal comparison it is impossible to translate this power into anything meaningful. Energy might be best used to compare how hard a firearm will recoil. Generally speaking, the more energy produced, the harder the gun will kick. Energy cannot be used to determine if a bullet has enough power to kill something. It is an old gun writer’s tale and a myth that you need 1000 foot-pounds of energy to kill a deer.

Trajectory

Explains the path of the bullet. This path can be drastically manipulated by the way a gun is sighted in. Here is a bit of information you may not know: all bullets fall to the earth at the same speed. Fire a 30-30 and a 22-250 rifle with the bore horizontal to the earth and both bullets will hit the ground at the same time. The difference is that the 22-250 bullet will travel a lot further before it hits the ground.

Sectional Density (SD)

This frequently referenced term is about as useful as a blind basketball referee. It’s nothing more than a numerical representation of a bullet’s weight, compared to its diameter. It is obtained by dividing the bullet’s weight in pounds by the bullet’s diameter in inches, squared. Some believe that all things being equal – they never are – the bullet with the highest sectional density will always penetrate the deepest. If you’re talking about non-expanding bullets this hypothesis will generally apply, but with expanding bullets it’s mostly irrelevant. The only SD that matters is the SD of the expanded bullet and that is controlled by bullet construction, velocity, and what the bullet impacts. Just so you know, a 150-grain .30-caliber bullet made of lead has the same SD as a 150-grain .30-caliber bullet made of milk chocolate.

Ballistic Coefficient (BC)

This is sort of a magic number that expresses a bullet’s ability to overcome resistance during flight. The higher the number, the less resistance the bullet encounters. If two bullets start at the same velocity, the one with the highest BC will travel further before it hits the ground. You might also say BC expresses a bullet’s ability to retain velocity and resist wind. Unless you are shooting at distances beyond the maximum practical range of your cartridge, BC is about as important to your shooting as seeing Trump’s tax return are to your enteral happiness.

Stopping Power

This made up term means absolutely nothing. Gun writers use it to explain things they do not understand and hunters utter it with reverence when they are sitting around campfires. Delete it from your vocabulary. For more on stopping power, click HERE.

Chamber Pressure

This represents how much pressure is generated inside the chamber of a firearm when a cartridge is fired. It is very important and very difficult (read expensive) for the average shooter to measure. Chamber pressure is why reloading manuals were invented and why you should always follow them. Too much chamber pressure is like having an affair; bad things are bound to happen.

Terminal Ballistics (Performance)

This represents a bullet’s ability to penetrate things and damage tissue. It is dictated by velocity and bullet construction. Two bullets that have identical unfired weights can produce drastically different terminal performance. Many erroneously base terminal performance on bullet weight. This is a mistake and will lead to trouble, just as if you asked a woman who is only fat, when her baby is due.

Penetration

This is most often reflected by how deep a bullet will drive inside a block of 10% ordnance gelatin. Sometimes 20% gelatin is used with rifle bullets because it takes half as much gelatin, or because the person doing the testing thinks it better represents animal tissue. The only thing you really need to know about penetration is that you must have enough of it. That depth obviously varies depending on what you need to shoot and the type of shot you take.

Expansion

This term should probably be replaced by deformation because bullets actually deform rather than expand. Bullets that deform, damage more tissue than those that don’t, but they also penetrate less. There is no ideal amount of expansion but anything is usually better than nothing. Something between 1.5 and 2 times the original diameter is often what bullet makers strive for. Given sufficient penetration, the more expansion, the better.

Recovered Bullet Diameter

We all like to pull bullets from animals and see that they have deformed with a wide front. Man oh man this looks good in photos and we can measure the diameter and brag about it. The truth is, pulling a bullet from a dead animal will tell you much less than looking at what the bullet did inside the animal. And, expanded diameter by itself can in no way be correlated to how well a bullet will kill. Pulling a good-looking recovered bullet from an animal is mostly confirmation the animal is actually dead.

Recovered Bullet Weight

The importance of the recovered bullet’s weight is one of the great fooleries ever presented to shooters. Unless that bullet is made of gold or some other precious metal, its recovered weight is of no consequence. Well, if you are shooting lead bullets and plan on reusing the bullet it might matter. In most cases a bullet that retains all of its weight will not damage as much tissue as a bullet that sheds some of its weight. And, in many cases, a bullet that retains all of its weight will not put animals down as fast. It’s not about how much weight a bullet retains, it’s about how much tissue it destroys. In an effort to create bullets that would shoot through barriers for law enforcement, weight retention became important. Ultimately, hunters adopted that high weight retention notion because, well, it just seemed like a damned good idea.

Accuracy & Precision

Accuracy and precision are two terms that are frequently confused. Accuracy references the ability of a bullet to strike the thing the shooter was aiming at. Precision reflects the ability of a gun to place repeated shots onto the same point. If a rifle shoots a five shot group that measures less than an inch at 100 yards, then it is a precise-shooting rifle. For it to be an accurate rifle, the rifle must be able to direct the bullet to strike the point of aim. An accurate shot can be lucky, but an accurate rifle must be precise.

Shot Placement

Ah, at last we have arrived. Ballistically speaking, shot placement matters most. The problem with improving your ability to place a shot correctly is that it cannot be purchased over the counter. Therefore, ballistics become more important to the shooter/hunter who will not make time to learn how to pull a trigger. And, gun writers and ballistic geeks like me continue to get paid to write about ballistics. Everyone seems to want a better bullet; few seem interested in taking the time to learn to place them better.