If you exceed the requirement, you exceed the requirement.
Even if you exceed the
minimum requirement by 1.5", as in the example we're looking at, my point was that one can still do better, at least according to the FBI (CWL has that issue well covered). Penetration performance keeps getting better up to and including 18", after which it is estimated that practically every bad guy will have been penetrated completely. 17" would be slightly inferior, and 19" would be a slight waste but not inferior as long as expansion isn't compromised substantially.
The reason that the FBI has both an optimum and minimum requirement is that their test protocol takes into account the varying depth of penetration that any given load will achieve when passing through various barriers. If they could get a load that gives them a perfect 18" in every case, they'd certainly take it, but anything that gives them at least 12" in every case (and more in some) would still be worth considering.
I think 12-15" is ideal, personally.
And you're completely entitled to your opinion, as we all are. It just differs from that of the FBI, that's all.
18" is not considered optimum by the FBI, it is considered to be the upper end of their requirement.
It may be an upper bound of what is useful, but in this case performance keeps getting better until that upper bound is reached, after which it declines not because of penetration but the reduced expansion that is implied.
Very few modern defense rounds penetrate 18", including in .357 sig. 5.56mm doesn't even penetrate that deep in gelatin.
That's true enough, which is why they selected the Ranger Bonded/PDX1 180 grain .40 S&W load, which in the most common cases (four layers of denim and heavy cloth) penetrated an average of 21.8" and 19", respectively, in their tests. Expansion was still pretty decent, and of course it penetrated at least 12" in every test. I use the very same load for the same reasons they do.
By the way, the most legendary handgun stopping round of all time barely penetrated 10" in FBI gel tests. The Fed/Rem .357 Magnum 125gr SJHP.
Well, there's legend and then there's measured, demonstrated performance. Obviously actual performance in human targets is going to be subject to many unpredictable variables, and is very difficult to analyze as well, but controlled, calibrated gelatin tests at least tell us how different loads compare to one another so that we can see and decide for ourselves which would give us the greatest odds of success overall.
