Bullets and the Human Body
Written by: William K. Smith III
There is a lot of misinformation, antiquated lore, and flat out lies (thank you, marketing) regarding firearms, bullets, and how they stop threats. Instead of relying on anecdotal evidence (“Back in the sandbox, I killed 35 insurgents with a Beretta M9 shooting FMJ, I don’t need no hollow points!”), data that is no longer relevant (“The .45-70 is responsible for winning the west, and winning my heart!”), or misinterpretation of data (“I read a study where .22LR had killed the most people, so caliber really doesn’t matter!”) why won’t we instead look at empirical evidence with repeatable, reliable, and consistent results? Science. Proven science. Or we can continue to hope and embrace cognitive dissonance – your choice.
Before we get into the nitty gritty of ballistics and what all these bare gelatin tests mean, we need to establish an understanding of what is required exactly in order to stop a human threat. To paraphrase D.R. Middlebrooks, there are three things that will stop a bad guy – when he runs out of blood, brains, or balls. What we mean by that is bleeding out, disrupting communication from the brain to the body, or simply intimidating/scaring them enough to run away. Another consideration in this equation is the fact that rifles and handguns typically achieve this goal in two separate ways.
Both weapon systems apply a projectile against tissue violently. If we look at the weight of common loads for fighting guns in both handguns and rifles, we will find that the weight of the handgun bullets often dwarf the weight of the rifle bullets (current U.S. Forces loadout for example, Beretta M9 pistol shooting a (usually) 115gr FMJ 9mm bullet and the M16A4/M4 shooting a 62gr FMJ 5.56mm bullet). If we’re talking about the author’s favorite guns to shoot, we see the 1911 pistol shooting a .45 ACP is typically a 230gr FMJ bullet and the AK-47 rifle shooting a 7.62x39mm is typically a 124gr FMJ bullet.
We can quickly and easily see that the weight of handgun bullets can and often do outweigh your typical fighting rifle bullets. But numerous studies conclude that rifle wounds are much more grievous than handgun wounds – so there must be another factor outside of just weight of the bullet. That factor is velocity. Rifle cartridges typically come screaming out of that gun two to four times faster than common handgun loads. The simple formula for Kinetic Energy (meaning, the amount of energy an object possesses while in motion) is one-half mass times velocity squared. This immediately tells us that speed is a much greater factor when it comes to energy than mass (though mass does play an important role in momentum, which we’ll talk about later).
Using our examples from earlier, we will examine the 9mm Parabellum and the 5.56mm NATO cartridges. The 9mm Parabellum comes out of an M9 at 1,250 feet per second. The 5.56mm NATO comes out of the M4 at 2,900 feet per second. This is muzzle velocity – meaning the speed that cartridge is coming out of the barrel of the gun (it immediately begins to decrease in velocity). Because we don’t live in a vacuum, we must also consider gravity (and humidity and elevation and a whole host of other factors if we want to be truly accurate in our figures). In order to express our formula in a way that can be understood, we’ll also convert the KE to foot-pound force. Our formula then looks like this:
Using this simple math, we can come to the conclusion that the M9 has 398.90 ft-lbs of energy and the 5.56 NATO has 1157.55 ft-lbs of energy. Huge difference! Why is that important? Well, when it comes to tearing and destroying tissue, the more energy we dump into the body the more damage that will be done. We can see that even the wimpy 5.56mm has nearly 3x more energy than the 9mm (and the author’s favored fighting rifle’s caliber weighs in at 1,607 ft-lbs bwa hahaha!).
Kinetic energy is certainly not the end-all be-all factor of stopping power, however, it is a useful metric to start with as it is an important factor for generating permanent and temporary cavities. For a quick comparison to other handgun calibers, let’s look at the common .40 S&W (180 grains moving at 1050 feet per second gives us 440.5 ft-lbs) and .45 ACP (230 grains moving at 980 feet per second for 490.38 feet per second). Makes your .25 ACP (45 grains moving at 815 feet per second for 66.35 ft-lbs), .380 ACP (95 grains moving at 980 feet per second for 202.54 feet per second), and .38 Specials (158 grains moving at 770 feet per second for 207.96 ft-lbs) seem pretty pathetic (hint: because they are). Let’s not forget our formula for 9mm earlier was for the cartridge the military uses, law enforcement and civilian populations should be using a hollow point loaded for self-defense (a Gold Dot 9mm is 124 grains moving at 1220 feet per second for 409.72 ft-lbs of manstopping).
And even then, there are endless accounts of single rifle shots (and even the mythic .45 ACP) to center mass not taking down a threat immediately. A determined assailant will continue to attack until they are out of blood, brains, or balls. Is it going to hurt? Yes. Is it going to kill the assailant? Probably, eventually. Is it going to stop them immediately before they can hurt you? Not likely. The average person can remain conscious for around two minutes even with traumatic blood loss. John Allen, an Army Soldier, attacked an Oregon State Trooper and was fatally wounded by that officer. The Oregon State Troopers are issued a Glock 22 .40 S&W Pistol. Allen was able to get up, reload his pistol and drive half a mile before he died. If he had decided to, he could have continued his assault against the officer. The average assault lasts thirty seconds to one minute. If I need to do that math for you as well, I’m going to ask you to give me three easy payments $99.95 before I continue.
So if relying on the assailant to run out of blood isn’t a reliable standard that leaves us with brains and balls. Everyone responds to stimuli differently, we all have different psychological make-ups and this then rules out relying on psychological stops. That leaves us with interfering with the central nervous system. The two methods firearms do this are by overloading the system with traumatic injury, and by removing the central nervous systems ability to communicate with the body and brain (damaging the spine, for example).
Handguns and even most rifle cartridges do not cause enough damage to reliably overload the system. Even though hollow points, tumbling, and fragmentation can certainly up the damage factor it is not enough to do so consistently particularly when you consider the multitude of variables they are going to face (clothing, armor, muscle density, bone density, fat, et cetera of the target). This means that the only way to reliably and certainly cause an immediate physical stop is to damage the spine or brain. Not so conveniently, our bodies are designed to protect these vital parts (weird how that works out).
This is why you hear so much jaw flapping about penetration. The International Wound Ballistics Association requires between 12.5” and 14” of penetration into ballistic gelatin for optimal performance for a bullet intended to be used defensively against the human animal. If it fails to penetrate that far it is inadequate, and if it penetrates more, it is okay but not optimal (for reasons of momentum transfer). “But Will, I’m not even 14 inches thick, why does the bullet need to penetrate that far?!” Well, because fights are fluid and you will not always be striking straight on the target. It’s more likely you will hit at some odd angle or have to go through an arm before it goes through the chest (as the assailant will likely have his or her hands in front them holding a weapon).
Let’s look at the penetration of our exampled Beretta M9 into naked 20% ballistic gelatin – we see that the average penetration depth is around 24.5”. This is quite a lot of penetration, and the reason why we want to use hollow points as civilians or law enforcement for stopping threats (the military has a different mission and a whole different set of rules of engagement). There are multiple reasons why over penetration is bad – the two primary reasons being we lose momentum transfer (if it’s passing through someone, we have not dumped as much energy, aka damage, into them as possible) and because we do not want to harm anyone or anything that is beyond our target (know your target and what’s beyond it – even the most reliable rounds can over-penetrate given the right circumstances. Mitigate this danger!).
Now let’s look at a few common defensive handgun loads and their penetration into the bare ballistic gelatin. The following calibers listed will all be variants of Speer Gold Dot for numerous reasons, not the least of which is proven consistency. The 9mm 124gr +P load sees an average of 11.78” of penetration, the .40S&W 180 grain load sees an average of 12.19” of penetration, and the venerable .45 ACP 230 grain load sees 13” of penetration. The .38 Special 125 grain +P sees an average of 11”, and the notorious .380 ACP Hornady FTX 95 grain (best consistent performer) saw an average of 11” of penetration. Against bare gelatin, there truly isn’t a lot of deviation and hardly any of the loads are meeting those minimum standards! What gives?!
Well, the clever developers and researchers that craft our self-defense loads realized that most gun fights do not occur between naked individuals (while a North Carolina inmate proved it was possible to holster a weapon while naked, most of us would fine this inconvenient). Against IWBA “Heavy Clothing” with those same loads we see the 9mm penetration increase to 15.88”, the .40S&W penetration became 14.10”, the .45 ACP became 14.55”, the .38 Special penetrated to 13”, and the Hornady FTX .380 ACP actually decreased to 8”. Again, the variation is negligible but we do see that these calibers are performing up to acceptable standards (except, you know, the .380 ACP).
Rifles and shotguns are an entirely different (though related) subject. Most common fighting rifle calibers are designed to tumble, yaw, or fragment when they meet a soft fleshy target. Some are even designed to penetrate through light armor, then do their nastiness. Our M855 5.56 NATO round has a lot of criticisms, but improvements are being made constantly with new generations (and when it becomes reliable and consistently deadly, the author will advocate it over the 7.62x39mm Russian).
If our shot placement were 100% perfect every time all the time, truly penetration (and reliability) would be about the only factor that mattered for self-defense loads. Since we are human, and we do err, and the inherently chaotic nature of violence puts us in less than ideal situations… we must not rely on getting that perfect shot off every time (but do not let perfection be the enemy of improvement – train to do as best as possible!). Thus we care about things like expansion (causing bigger holes inside of people) so we can attempt to cause enough damage to end a fight sooner, if not now. This is why we care about things like follow-up shots (each shot, with a practiced shooter, increases our chances of getting that physical stop). And this is why capacity is important, too – ballistic figures show us that if all we knew we only had one then we’d be best off with a .357 Magnum out of a 6” barrel (125 grains moving at 1450 feet per second and averaging 15.65” of penetration).
But that is not reality, we do not live in a vacuum.
If you want to carry a .380 ACP as your primary means of self-defense that is entirely up to you. The author cannot advocate it, he will talk until blue in the face as to why you shouldn’t, but at the end of the day it is entirely up to you. The vast majority of reputable reality-based self-defense instructors across the nation recommend a 9mm +P or +P+ for a reason. It is not because they are marketing a product to you (like your local gun shop probably is, and like the firearms and ammunition manufacturers certainly are), it is not because they are relying on anecdotal, unproven information, and it is not because of ego. It is science. Repeatably proven, consistent, and reliable science.
Fight with the right tools, the right mindset, and always… Train to Prevail!