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Caliber and Terminal Ballistics

Chris Upchurch


Debates over caliber and terminal ballistics seem to be one of gun guys’ favorite pastimes. If you hang around any gun shop you will find guys debating the merits of 9mm versus .45. If you examine any online gun forum, you will find countless posts devoted to the minutia of terminal ballistics. I can tell you the core of what you really need to know in three words:

Pistol bullets suck.

The truth is for all the energy expended on these debates the truth is none of the realistic options are very effective. We carry pistols because they are handy and easily concealable, not because they do a very good job at stopping an attacker. If you want something truly effective, get a rifle or a shotgun. Since most of us cannot carry a rifle or shotgun around all the time, keep in mind the following corollary to the fact that pistols bullets suck:

Repeated application may be necessary.

That’s all you really need to know. Of course, I’m not going to stop there, but that is the gist of it.

Before I move on, I do want to explain one thing: Terminal ballistics are not terminal in the sense of a terminal disease or Arnold Schwartzanegger saying, “I'm a Terminator.” They are actually terminal in the sense of a bus terminal or an airport terminal. As in place where a journey ends. Ballistics can be divided up into three phases: internal, external, and terminal. Internal ballistics describes the behavior of the bullet inside the firearm as it accelerates down the barrel. External ballistics describes the behavior of the bullet in flight. Terminal ballistics describes the behavior of the bullet inside the target.

Fundamentals of handgun terminal ballistics

In many of the gun store and internet debates you will hear people talking about things like energy dump, hydrostatic shock, and knockdown power. These range from irrelevant to complete bullshit.

‘Knockdown power’ falls on the bullshit end of the spectrum. As Newton’s Third Law states, “For every action there is an equal and opposite reaction.” If the bullet has enough force to knock the target down, that same force would be applied to the shooter as recoil. To oversimplify a bit, if you didn’t get knocked down from firing the shot, don’t expect the bullet to knock your target down simply because of it’s impact.

Hydrostatic shock, on the other hand, is a real phenomena. It just doesn’t have any application to handgun rounds. In order for hydrostatic shock to have an effect on tissue you need a very fast projectile, one traveling at least 2000 feet per second. This is far faster than any of the handgun rounds we’ll be discussing here, but it is something that we’ll return to in the future when we discuss rifle terminal ballistics.

The truth is pistol bullets are like a long range drill. They are a means of boring holes through a target. The key to incapacitating an assailant is putting these holes in the proper places.

Methods of stopping an attacker

There are four main methods for stopping an attacker using a firearm: fear, pain, lowering the blood pressure to the brain, and severing the central nervous system.

Inducing fear in the attacker is actually by far the most common way firearms are used to stop a criminal attack. Most ‘uses’ of firearms for self defense don’t actually involve any gunfire. The intended victim produces a handgun and suddenly the attacker decides this all was a very bad idea and he needs to leave as quickly as possible. This happens hundreds of thousands of times a year.

This is all well and good. Actual gunfights are dangerous and have financial and legal consequences afterwards, so if we can get out of a situation without shooting it’s all for the better. The problem is that fear is not a reliable method of stopping an assailant. While it works most of the time, it does not work all the time. Fear tends to work best on criminals motivated by financial gain, rather than those who act because they enjoy having power over others or have a specific grudge against their intended victim. Many criminals have had guns pointed at them before, they’re used to it. Finally, fear requires that the criminal not only see the gun, but perceive your willingness to use it. Criminals know that many people are not willing.

Pain, on the other hand, certainly gets past the question of your willingness to use the gun. Getting shot does take the fight out of a lot of people. Unfortunately, it’s not completely reliable either. Many criminals on the street may have been shot before and survived. The attacker’s sense of pain may be impaired by drugs or alcohol, or they may just be hopped up on adrenaline a fight or flight reaction. They may not even realize they’ve been shot. They may simply be very determined and willing to fight through the pain. Whatever the case, while pain may stop some attackers we cannot totally rely on it.

Moving into the realm of physically incapacitating an attacker, the most common way to accomplish this is to lower the blood pressure in their brain to the point that they loose consciousness. One way to do this is simply to let enough blood out that the heart cannot keep their blood pressure high enough to maintain consciousness. The problem is that this takes time. Even if you completely sever a major artery like the femoral it can take over a minute for them to loose consciousness. They can do an awful lot of bad things to you and your loved ones in that minute.

A faster alternative is to stop the pump by destroying heart, although even this won’t lead to instant incapacitation. With the blood supply to the brain completely cut off there is still enough oxygen in the brain tissue for 10-15 second of useful consciousness. The heart is also not the easiest target to hit, being fairly small (about the size of a fist) and protected by the ribcage.

The only way to instantly stop an assailant is to destroy or sever a critical part of the central nervous system. The main target for an instant ‘lights out’ stop is the brain stem. Simply hitting the brain is not always good enough. A surprisingly large portion of the human brain isn’t necessary for simple mechanical tasks like pulling a trigger (see for example a hemispherectomy .

The brain stem is not a very large target (it is about the same size as the thumb). It is deep within the skull, the bones of which are thick and sturdy enough in places to deflect handgun rounds. Compounding the problem is the fact that the head moves considerably more and quicker than the body, making an accurate shot even more difficult.

If we cannot destroy the critical part of the brain, we may be able to cut it off from the rest of the body by severing the spinal cord. Again this is not an easy target. The spinal cord is about the diameter of your little finger, placed near the back of the body, and armored by the surrounding bones of the vertebral column. When severing the spinal cord to stop an attacker, higher is better. A shot directly below the brain stem is, for all intents and purposes, as good as a brain stem shot. Generally a hit above the shoulder level will paralyze the hands, leaving it impossible to manipulate a weapon. Spinal cord damage lower than this will eliminate mobility, but the assailant may still be a threat if they are armed with a firearm.

This may seem rather depressing for someone looking to defend themselves. Given the inadequacy of handgun bullets and the sheer difficulty of quickly physically incapacitating an attacker, how can we effectively stop an assailant? The solution, as mentioned earlier, is repeated application. A single shot may be unlikely to produce instant physical incapacitation, but five shots in the chest or the face are much more likely to have the desired effect. Multiple shots make it easier to hit small, difficult targets and increase the odds of getting through bone and other biological armor that protects the heart, brain, and spinal column.

Target areas

Our primary target zone is the upper chest, the ‘Golden Triangle’ between the nipples and the base of the neck. This contains not only the heart, but also many major arteries and, at the back of the body, the spinal cord (though a hit at this level will only eliminate mobility, not necessarily the ability to use a weapon).

Our other major target zone is the face. Because of head movement this is more difficult to hit. If hits to the torso are not doing the job, if the torso is not visible, or if you are close enough and confident enough in your marksmanship that you can hit the face as quickly as you could hit the upper torso, shoot the attacker in the face.

Specifically, we want hits between the mustache and the eyebrows. This is at the right level hit the brainstem, and we also benefit from three large openings in the front of the skull (eyes and nose). Above the eyebrows, the forehead is one of thickest and strongest parts of the skull. Below the bottom of the nose, the teeth are the hardest objects in the human body. Both of them can do strange things to the trajectory of handgun rounds (remember, pistol bullets suck).

One thing to keep in mind is that unlike the flat targets we practice with on the range, the human body is three dimensional. The real target is not the bridge of the nose or the second button on their shirt, those are just reference points that work when the target is squarely facing you. If the target is not facing you, you need to pick a different reference point.

The brainstem is essentially directly between the ears.



The heart is located in the middle of the chest, centered in the body front to back.

If the target is behind cover, sometimes only part of the target will only be visible. In that case, we need to take what we can get. Shoot the center of whatever part of his body is visible. Any shot on an adversary, even if it’s just an elbow or foot, is good for you and bad for him. It may successfully stop him through pain, it may diminish his fighting ability even if it doesn’t stop him, or it may distract him enough for you to get a more conclusive shot.

Some firearms trainers advocate the pelvic shot as an alternative to the head shot, a few even claim it is superior. The idea is that a shot that breaks the pelvis will destroy their mobility and prevent the assailant from walking. The problem with this is that the pelvis is a very heavy, solid piece of bone. It is not likely to be broken by a pistol bullet (remember, pistol bullets suck). Furthermore, the pelvis is a ring structure, in order to completely eliminate the target’s mobility it must be broken in at least two places.

None of this is to say the pelvis is a poor target. It hosts several major arteries, the nerves that control the legs, and some significant organs. However, the instant destruction of a target’s mobility by a pelvic shot as promoted by some instructors is not very realistic.



Choosing a caliber

As we have established, pistol bullets suck. Some would argue that given their suckage, you should choose the largest, most powerful round available. The truth is all pistol bullets suck about the same.

Gun store groupies and keyboard commandos will go on and on about energy and knockdown power, but remember, pistol rounds are like a drill. They make holes. To physically incapacitate an attacker, the hole needs to intersect a major artery, the heart, or the central nervous system.

When we are choosing a caliber, we are choosing the width and depth of the hole. The bigger the caliber, the wider the hole. The faster and more massive the bullet is, the deeper the hole.

There is a point of diminishing returns to the mass and velocity of a handgun round. If the hole is deeper than the target, the bullet will keep going out the other side. We want sufficient penetration to reach the vitals, but lots of extra penetration does not do us a lot of good.

In terms of width, all of the realistic choices are between .35 and .45 inches in diameter. That’s a difference of one tenth of an inch. Will that tenth of an inch really make a difference? Probably not. A hit to a major artery, the heart, or the central nervous system will not be significantly more effective. A larger round might convert a near miss on one of these into a grazing hit, but that would require you to miss by less than 1/20th of an inch.

Any marginal difference a larger caliber round might make has to be weighed against the disadvantages. Larger rounds mean fewer rounds in a pistol of the same size. It may seem like six or seven rounds would be plenty, but remember the advice given above regarding multiple shots. We’re talking about shooting an attacker five times in the chest, followed by another five in the head if the shots to the chest didn’t do the job. A seven shot pistol might not even suffice for one guy! Combine this with the fact that more than 50% of robberies involve 2 or more attackers, and 24% involve 3 or more (National Crime Victimization Survey) and a 7 round handgun quickly begins to seem inadequate.

The other disadvantage of the larger, more powerful calibers is their greater recoil. This also relates back to the idea that repeated shots may be necessary. How quickly can you deliver that burst of five rounds? Keep in mind that in a dynamic situation like a gunfight you may not have a chance to get a full two-handed grip on the gun, properly brace yourself, etc. You may be firing those rounds one handed, using your non-dominant hand, from an unusual position or while moving. How quickly can you shoot a larger caliber in those conditions?

So, we need a round that provides sufficient penetration to reach the target’s vitals, but excess size, mass, and velocity doesn’t do much, and the extra recoil and lower capacity make them a poor tradeoff. That round is the 9mm. It occupies the sweet spot between excess power and insufficient penetration.

For a fuller discussion of the available options, see the companion article on Handgun Calibers.

Self Defense Ammunition

In many ways, the equipment we carry for self-defense isn‘t that modern. We use cartridges that go back over 100 years and the handguns we use today aren’t that different from those in use decades ago. However, one area of fighting with firearms that has seen substantial improvement in recent years is ammunition. We have gone from hollowpoint bullet designs where, if you’re lucky, you might get some expansion to bullets that will expand with monotonous regularity.

Earlier I said that a handgun acts like a long range drill, the bigger the caliber the wider the hole, and the faster and heavier the bullet the deeper the hole. Expanding ammunition essentially lets us trade off depth for width. As the bullet expands, it’s going to slow down quicker, but it will make a wider hole. All of the service pistol rounds mentioned above have considerably more penetration than necessary when fired with non-expanding full metal jacket (FMJ) ammunition. Using expanding bullets allows us to trade away some of this penetration for a larger hole, without reducing capacity or increasing recoil.

Almost all expanding ammunition works the same way: when it hits the target the open tip of the bullet gets filled with flesh, which forces the outer edges of the bullet to open outward, like a blossoming flower.

These days, almost all expanding ammunition is designed to meet the same specification: a series of tests promulgated by the FBI where the bullet must achieve 12" of penetration in ballistics gelatin under a variety of conditions. Any self-defense ammunition from a major manufacturer (Federal, Winchester, Speer, Cor-Bon, DoubleTap, Hornady, or Remington) should meet this spec.

Don't buy gimmick ammo. Anything with “Extreme” in the name is probably a bad idea. Stay away from super high velocity ammunition. Every few years, someone gets the idea of using very lightweight bullets for a given caliber to achieve very high velocities. Light, fast bullets have very high energy, and the manufacturers will often brag about how much energy their ammunition produces. Remember what I said earlier, energy by itself doesn’t mean much for pistol rounds. The critical thing is the ability to penetrate deeply enough to reach the vitals. Thanks to their light weight, these high velocity rounds don't do a very good job penetrating compared to more conventional ammunition.

Second, stay away from frangible ammunition. Frangible bullets are designed to break up when they strike a target. They can produce some truly horrific wounds, but these small pieces don’t penetrate as deeply as a single, larger projectile. Frangible bullets often fail to penetrate deeply enough to reach the vitals.


One disadvantage of using calibers designed over a century ago (.38 Special, 9mm, and .45 ACP) is that they were designed to operate at relatively modest pressures. Modern firearms are stronger and can take more pressure, thanks to the better designs and metallurgy that are possible today. To take advantage of these advancements ammunition manufacturers make +P ammo that operates at higher pressures and achieves somewhat better performance. Because +P ammo operates at higher pressures than the caliber was originally designed for, you should only use it in firearms that the manufacturer specifically rates for the use with +P.

Going to +P ammo is kind of a halfway step. It’s not going to provide all of the benefits of going to a more powerful caliber (9mm to .357 SIG or .38 Special to .357 Magnum), but it doesn’t have all of the drawbacks either. +P ammunition will not reduce the capacity and any increase in recoil will be fairly modest compared to stepping up to a bigger caliber. In a full size or compact pistol there are few drawbacks to using +P ammo. Smaller semi-autos are already pretty snappy and going to +P will only exacerbate this. .38 Special is already fairly mild even in smaller, lighter guns, so using +P ammunition does not produce excessive recoil.


While I have delved quite a bit into the minutia of terminal ballistics, anatomy, cartridges, and ammunition, the basics of caliber and terminal ballistics are pretty simple: Pistol bullets suck, repeated application may be necessary. A pistol is like a long range drill, it makes holes. Beyond a certain point, wider and deeper holes aren’t that useful against a human target, meaning all pistol calibers from 9mm up suck about the same. The key is making sure those holes intersect something vital.