Commercial ammo from FN won't penetrate vests, one variant would go through some lower threat level vests by virtue of velocity, but that one is no longer sold. One can buy special loadings from other companies that do better than FN's ammo, runs faster etc. I failed to trade into one of the 5.7 pistols a few months ago, got a Sig 556 instead.
FN keeps their AP stuff in a special bonded warehouse and only releases it for LE/Mil agency purchase orders. However other companies make rounds that still have good AP properties by virtue of velocity/bullet construction of a non regulated nature. In short it works like AP, but becuase of how it works, the ATF doesn't restrict it as AP handgun ammo.
However, even the AP rounds will only penetrate soft body armor. Any sort of rifle plate defeats it. It also has limited tissue penetration, perhaps too limited, once it is through the armor.
Welcome to EliteAmmunition.com is the source for most of the better/hotter/more interesting loads.
I wouldn't bother with an AR upper so chambered personally, since I don't get the point (why wouldn't I just use 5.56mm?), but I'd be willing to experiment with one of the pistols.
But in general, the given niche is shooting through soft armor and rifles still do a better job for that.
