That type of a position is something I am familiar with, but the question that is not clear to me is whether penetrating body armor, be it kevlar or plates is a fundamentally different process than going through typical barriers like walls and car doors (and soft tissue).
A sort of an anecdotal piece of information I have some personal familiarity with is that the slow moving 7.62x39 goes through walls and other natural barriers a fair bit better than much faster moving 5.56x45. Sectional density of the much slower moving 7.62mm 123gr bullet is roughly equivalent to that of a 65gr 5.56 bullet.
However, in that case, with comparatively simple bullet construction, there may be an effect from a faster moving bullet deforming faster which impedes barrier penetration. Alternatively (or additionally) momentum may be a significant factor since 7.62x39, depending on specific ammo, does have abut 40-50% higher momentum.
As I said, it is not my field, so I'll ask some questions and do some digging. I do work largely with the DOD and prime contractors, so there enough people I can ask.
ILya
