This is a discussion on Bullet Penetration within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; Originally Posted by Majorlk In the vast majority of shoot-outs, it's not the bullet that exits the target that is of primary concern; it's the ...
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For one thing the FBI and Duncan do not say 12" of penetration is the perfect number. They say 12" is the minimum and 16" or 18" is the maximum. Too many people assume that 12" is the perfect number when it's actually the least amount of penetrations that will pass protocol.
Duncan's book is very informative but he doesn't just focus penetration he also focuses on expansion or making the biggest hole while penetrating deep. His point is that there is no energy dump, no shock. That the only way to reliably stop a bad guy is to make big, deep holes so that they bleed out fast.
Too many people get hung up on over penetration and assume that the 12" penetration is because we don't want a bullet to pass through a bad guy. That's incorrect The 12" to 18" are there so that the bullet will reach the vitals at all angles, even when going through arms, shoulders etc. Statistic of officer involved shootings show that 85% of your shots will miss the target so over penetration is the least of your worries.
One other thing, while a bullet that enters skin does so easily exiting skin is another thing. It is much tougher for a bullet to exit the body than it is to enter and while a bullet might penetrate 18" in gel it might go through a body but get stuck on the opposite side because it didn't have enough energy to exit. Think of it this way.
A package of ground meet with that clear plastic wrap, pull it tight then stick your finger through it into the meat. Now pull it tight hold it so that there is nothing to push up against but the wrap and stick your finger thourgh it. It's much harder to poke a hole through because the wrap stretches more. Skin will also behave like this. A bullet exiting will run into the same elastic effect when encounter skin on the opposite side of the wound.
agalindo is correct -- 12" is the minimum. Bare minimum. I think what people get hung up on is they think that 12" of gel penetration is the same as 12" of body penetration. It's not -- it totally isn't. As an example -- a BB gun, at 590 fps, is used to calibrate ballistic gel. That BB should go about 3.35", up to 3.75", into the gel. But how far would a BB go if you shot it at a person's chest? It's likely that it wouldn't even break the skin.
A bullet that has enough power to travel 18" of gel, also has enough power to reach the vital organs, and pass through them, with enough velocity that it can seriously damage them.
But it's not like it'll go overpenetrating a body. More than 18", yes, that becomes a possibility. But if you have a bullet that can reach 18" in gel, that shouldn't go overpenetrating a human (even though, yes, we all know that humans are only about 10" to 12" thick, front to back, but -- again -- penetration through a body is not the same as penetration through gel. Gel doesn't have bones, for one thing.)
I would suggest not putting much stock in anyone's advice who tells you that you MUST have X inches of penetration, etc. Nonsense. The objective is to disrupt the Central Nervous System. That's how you stop a human. The movies and TV do everyone a disservice by suggesting that everytime someone is shot, they drop right there. It doesn't happen that way. Understand what Critical Mass is and how it is vital to shutting down the CNS. A 6" penetration in the correct places is a far better outcome than 12" where it won't have a stopping effect. Placement is the key, not inches. The misinformation you can find on this topic floating on the Internet, and by book authors without a clue, is amazing and sad.
Placement is vital, but so is penetration. A perfectly placed shot that penetrates 2" will be no more effective than a lousy-placed shot that penetrates 12".
Shot placement isn't something you can buy, it's something you have to develop through experience. But penetration is something you can buy. Proper defensive ammo selection should factor in the IWBA and FBI specifications for penetration, yes, but the hugely important factor that people forget (or don't know in the first place!) is -- it has to deliver that performance FROM YOUR GUN. What does it matter if a bullet penetrates 14" from a 6" barrel pistol, if you're carrying a 3"-barrel pistol? The performance your pistol delivers, will not necessarily match the performance of the 6" pistol.
If you want to consider penetration, you have to see results of it being tested from a comparable length barrel as to what you'd intend to use it in. Many of the tests for defensive ammo on youtube, and many of DocGKR's tests, are from pistols with about a 4" barrel. So if you're carrying a 4" pistol, you can likely expect results comparable to what those folks got. But if you're carrying something significantly shorter, or significantly longer, then you're in uncharted territory and you should instead look for tests that were conducted from a pistol barrel length comparable to your own.
By no means, the book is full of verified terminal ballistics information. You just have to read it carefully. Like I posted, if you have read the whole book you will have noted that what Duncan is saying is:
1. Penetration is vital
2. Bullet shape is vital because the amount of tissue crushed and cut depends on bullet shape.
What you need it deep penetration and a bullet that has a shape that will crush the maximum amount of tissue. These are the the reliable wounding factors not the mythical energy dump, hydrostatic shock...
So what should you get from his book? Besides all the technical info about bullet shape and wounding.
If shot placement is the same the round that, penetrates deeper and expands to a larger diameter will crushes and cut more tissue and will stop an attacker sooner.