Frequent question I get asked, and one that I’ve tried to address before, is this:

“If a person’s chest is only 10″ thick, then why should a bullet have to travel at least 12″ and up to 18″?  Wouldn’t that just mean massive overpenetration?”

Seeing as I just had to answer that question again, I thought I would put the response here, so that it can be available as a reference for anyone interested.

The question is a simple one, and it has a “common sense” answer: anyone with “common sense” would see, obviously, that since the average person is only 10″ thick, and the vital organs are located in the middle, then obviously you’d only need a bullet that penetrates six or eight inches at most, right?

The problem with this logic, as with all the recent labeling of proposals as “common sense”, is that it’s based on faulty assumptions.  As with an example that I’ve used before, it’s just “common sense” to know that the sun revolves around the Earth, right?  People could see with their own eyes that the sun rises up, and then sets down, and revolves around the Earth, and the ancient church held it as heresy to say otherwise.  It’s “common sense!”  Except for the fact that it was wrong.

So in that context, we have to first dismiss the faulty assumption — and that faulty assumption is, that bullet penetration figures = body penetration.  They don’t.  A bullet that penetrates 12″ of ballistic gel will very likely not penetrate 12″ of a body.  Remember, ballistic gel is not a body simulant, it’s a soft tissue simulant, and bodies are made up of many more types of tissue than just soft tissue.  Some is firmer than others, and there’s of course those pesky bones too — bones won’t necessarily stop bullets, but they will slow them down more than soft tissue would.

So when we discuss bullet penetration, we have to divorce ourselves from the notion that the bullet under discussion will penetrate a body to the same degree that it penetrates ballistic gel.  They’re not the same, nor were they ever intended to be the same.  Now, if you’re asking about a bullet fired into muscle  tissue (such as a big meaty thigh) then yes, the penetration through muscle will be very nearly the same as the penetration through ballistic gel.  And, our bodies are pretty much entirely sheathed in muscle and it’s a fairly safe bet that any bullet impact is going to go through muscle, but even so, that’s not the whole story.  Suffice it to say that the penetration figures do not relate to body penetration, so you shouldn’t directly compare them.

Quit Blathering And Answer The Question!

Okay, with that disclaimer noted and out of the way, let’s go on to the question at hand — and, first, the question is: how deep in the body are the vital organs?  Unfortunately, there’s not a direct one-size-fits-all answer to that, because (especially among Americans) one size most definitely doesn’t fit all! It depends on what we consider “average” for a human.  Skinny small people, obese people, and very muscular people, are all going to have varying depths to the vitals.  In general, the average torso is somewhere between 10″ and 12″ thick.  The vital organs are located generally within the ribcage, and depending on which organ we’re talking about, it could be as close as 6″ for a straight-on, unobstructed shot (meaning, the target is lined up face-on like a silhouette target, and there’s no arms or other intervening obstacles to get in the way).

Right — so now that’s sorted, let’s again raise the question — if the vitals are only 6″ deep, why on Earth would you need a bullet to penetrate 12″?  And if the average person is only 10″ to 12″ thick, wouldn’t a 16″ or 18″ bullet totally overpenetrate right through them?

Again, stick with me and you’ll see that it all does make sense.  These are reasonable questions on the surface, but once you start adding it up you’ll see that in fact the actual situation is more complex.  First, you don’t want the bullet to reach the vital organs, you want it to disrupt or destroy the vital organs, and that means it has to penetrate deep enough and still have enough speed that it’ll be able to damage the vitals and not just come to a stop right in front of them.  So yes, the shallower vitals may be located only six inches deep, but that means you’d want your bullet to go at least 8″, so it has a chance to punch into the organ and disrupt it.

So an 8″ Bullet is All I Need?

No, that’s not what I said.  We’re just getting started!  Let’s do a little simple math — 6″ of penetration to reach the vitals, plus we want at least a couple of inches of damage travel so that the bullet will sink in and disrupt them, so that brings us to 8″, yes.  But we have to factor in that we will almost certainly need the bullet to bust through the ribcage since pretty much all the vital organs are located inside the ribcage (except for the brain stem, obviously), and from a prior study I’ve shown that it takes about 2″ off of a bullet’s penetration capability to get through bone, so add another couple of inches of penetration energy necessary to get through the ribs, and that brings you to needing an absolute minimum of 10″.

Okay, So — A 10″ Bullet Is Good Enough, Right?

Only in the most optimistic possible case — if it’s a straight-on shot — no intermediary obstacles such as arms; no odd angles.  Just you and the attacker, squaring up against each other like some Old West duel, each of you standing square on to the other, exposing your chest completely.  Does that sound reasonable?  Doesn’t sound reasonable to me!  If you get in a gunfight, are you just going to stand there and take it?  Probably not — and if you’re not going to, why would you expect your attacker to?  Hint — he won’t.

So now we have to talk about less-than-perfect situations.  If you have to take a shot from a different angle (such as that the bad guy’s knocked you down, so now you’re having to shoot upwards at someone standing over you) then maybe add another 2″ to 4″ of penetration depth necessary because now you’ll be firing through a longer path to get to the vitals.  And now, let’s add in an arm, because if the bad guy’s pointing a gun at you, the geometry of the situation pretty much dictates that his arm will absolutely be in the path between your gun and his vitals.  Getting through that arm may soak up 5″ of distance, plus another 2″ of penetration power necessary to get through the arm bone.

 Okay, But … Um … Oh, I see…

Yep.  That’s why the recommendation from the wound ballistics conferences were that for a bullet to reach the vitals, it would require at LEAST 12″ of penetration power through soft tissue, and preferably up to 18″ if you want the bullet to be able to perform in all conceivable shooting scenarios and from all angles (which is perhaps more of a priority for law enforcement, but isn’t strictly limited to law enforcement).

Remember, you won’t be able to choose your shooting scenario.  You can’t stop in the middle of a gunfight and say “Excuse me, Mr. Bad Guy, but — see, I’m not a cop, I’m not the FBI, so I didn’t buy that 12″-penetrating bullet.  I just thought I’d only need an 8″ bullet.  So, could you please stop moving and put your arms up so that I can get a clean unobstructed shot at your chest?”

Um, yeah, good luck with that.  I think a better plan is to just follow the advice of the experts who do this for a living, and shop for ammunition that reaches the performance parameters that they identified as necessary: a minimum of 12″ of penetration power through soft tissue, with a maximum of 18″ of penetration.  And make sure that the bullet will deliver that kind of performance from YOUR gun!  Don’t go viewing tests that were performed from a 5″-barrel pistol, and think that you’ll get the same performance from a 3″ barrel, because you almost certainly won’t.  Use ammo that performs to the standards from your gun.  After that, it’s just a matter of placing the shot where it counts — or, preferably, be somewhere else before the bullets start flying.