skribs said:
I've noticed a lot of loads that are designed for personal defense, put out by a lot of companies, either fall short of or barely meet the 12" penetration requirement in ballistics gel. IIRC, the FBI recommends 12-18", and I'd personally prefer something on the later end. It seems form comments on the various ammo that a lot of people agree with me. Too often I see "it's a good idea, but the load is light and likely to underpenetrate" or "it only has 11 inches of penetration, I wouldn't use it."
I think Sam hit the nail on this one... the less effective bullets are sold to satisfy the desires of a market segment that is terrified by the idea of over-penetration. But, reality is that a bullet that penetrates deeply enough to do its job is going to be a bullet that can also penetrate wall board and other such objects (as such, hitting your target does minimize this risk a bit).
allaroundhunter said:
The 12" minimum is because law enforcement engagements oftentimes include shooting through barriers. Civilian SD encounters rarely do.
There is no part of the human body that requires a bullet to travel 12" to reach vital organs, so I don't require my self defense rounds to pass that test.
Except that the 12-18" penetration goal is AFTER the bullet has struck intermediate barriers such as windshield glass, etc (in other words, in LE we aren't looking for a deeper penetrating bullet because of these barriers, we are looking for that much penetration even IF we penetrate those barriers). As such, the only difference in what law enforcement may require is that their bullet still needs to maintain that level of effectiveness AFTER striking those barriers. The goal on-target is still 12-18" of penetration in calibrated (I believe 10%) ballistic gelatin.
Bullets do funny things. Sometimes a bullet will get deformed/clogged after going through a barrier (be it clothing, wall board, windshield glass, etc), and will then fail to expand, thereby penetrating more deeply. Other times a bullet may come apart and fail to penetrate as expected after striking an intermediate barrier (my department switched our rifle ammo after observing this trend during shots through barriers -- I was at the workshop myself, and wasn't thrilled with seeing 7" penetration from a .223).
As an example of why the 12-18" of penetration in calibrated ballistic gelatin guideline is used, consider the following shot:
An adversary that weighs 350 lbs is facing you from the side. The only shot you have toward the vitals involves shooting through the arm, before hitting the torso itself. First, you may very well need at least 12 inches of penetration on such a shot against a person who's that big, especially if you have to shoot through an arm to get to the vitals. Secondarily, you will quite possibly hit bone. The 12-18" is based purely on gelatin, whereas bone will most certainly change the real world performance.
In our wound ballistics workshop (which was put on by ATK) we conducted the tests in a standardized manner. The intermediate barriers consisted of things like windshield glass, wall board, light clothing, and heavy clothing, all per the FBI protocol. But, we also shot the gelatin without going through an intermediate barrier. The goal in each test was to land in the 12-18" penetration range.
loose noose said:
I prefer a light projectile that will expend it's energy in the intended target.
The whole concept of "energy transfer" with a bullet is meaningless. Don't get me wrong, I know you aren't the one who pioneered this idea. It has been talked about at gun store counters and in the halls of gun shows for years. Some companies even market to the idea. Put as simply as I can say it, the size and depth of the hole made by the bullet is what matters here (these things can be determined by the velocity of the bullet, the size of the bullet, the expansion of the bullet, and how the bullet stays together after making contact).
A bullet that stops short after a hit simply stops. It doesn't deliver any more practical energy to the subject than the bullet that zips on through. The idea of "knock down power" is great for marketing, but a poor thing to bet your life on. Simply put, a bullet doesn't just knock you down.