Originally Posted by Andy W
18.5' is a little too much penetration for civilian applications. Good chance of over penetration which is an issue for urban home defense. You don't wanna shoot through the bad guy and have the bullet pass through the wall ending up God knows where.
There is more to the break down on penetration than just simply 18.5 is too much. IMHO, people see that 12" mark as the only mark that is acceptable. Of course ballistic gel and it's variants are consistent media, there is no air space like what might be found in a lung, no difference in tissue like in the body and lastly, no bone. So, what can happen in the body can be different in gel, everyone knows this... or should. BUT, gel tests are the convenient consistency that most look at for an idea of what they want or feel they need. So to keep things convenient for discussion sake I'm going forward with my comments as if the gel correlates mostly to what you can expect for penetration on an assailant. This should be fair since the gel test is what feeds your apprehension for this loading.
I've explained it this way before so here goes...
Picture a thin individual, 8 1/2" from chest to back. Also envision a squared off shot opportunity (perfectly facing this notional BG). Once the shot is made, based on the gel test for comparison sake, we are going to allow 18.5" of penetration. The skin alone equates to roughly 2" of penetration value on the front because it is supported by tissue underneath and I would venture to guess the fact that the sectional density of the bullet helps since it is still unchanged (it has not expanded). The skin on the back (exit) side equates to roughly 4" penetration value (at this point the skin has room to move and the bullet is expanded, decreasing it's sectional density). At this point we already have 6 total inches accounted for. When we add in the other 8" (roughly) of body depth we are now totaling 14" of penetration value on our thin assailant. This would leave us with only 4.5" of unaccounted penetration value. The bullet, at this point, has a much worse sectional density which will make it more difficult to penetrate the skin of another unwanted target. It also would have a small chance of making it to the vitals.
Yes, I know that hitting any other
target is bad no matter how you slice it but it's not really the point. The main point is that given an extremely thin individual that bullet doesn't have much of an opportunity to cause harm. If that same notional individual turns slightly he would add even more penetration value. If he presents any limb in the way of the bullet, again, more value is added. Or if he is simply the average torso size of 9.4" or greater, is quartering away from you and presents arms in the path of your bullet... you have nothing to worry about.
Also note that I am not the more penetration is better
type. I don't really worry if a bullet doesn't reach 12". The biggest worry anyone should have is a miss.