Thoughts on armor piercing bullets in AR pistols?

[10x25mm]

If you're not a criminal, AP ammo is legal for you to own or use. There's a PDF on ATF's website that when they were talking about the M855 ban, that "It's perfectly legal for civilians to own AP ammo"

This is only true of M855 ammunition, which is not armor piercing under 18 USC 921(a)(17). 'Handgun' ammunition with projectiles found to be armor piercing under 18 USC 921(a)(17) is not legal to own and this prohibition is echoed in MCL 750.224c. BATFE has long found both 5.56x45mm and 7.62x51mm cartridges to be 'handgun' ammunition.

M1158/59, no one knows anything about. However M993/M995 has been around for awhile, and it's about $20-30 round to purchase.

The Nammo (formerly Bofors Carl Gustav) M993 7.62mm projectile has a sintered tungsten carbide (WC) core which uses a cobalt binder. This projectile is weakly magnetic due to the cobalt binder. Sintered tungsten carbide is not very effective as a penetrator and tends to shatter upon impact with most hard armors. Total weight of the M993 7.62mm projectile is 8.3 g, or about 128 grains. A lot of these projectiles have been pulled as the U.S. military has demilled their remaining stocks of M993 cartridges and are being sold in the civilian market. BATFE has not issued an official ruling, but it can be presumed that they would find that M993 7.62mm cartridges would violate 18 USC 921(a)(17). A technical case could be made that sintered tungsten carbide is actually a cermet and not an alloy, but courts are metallurgical idiots.

The M1158 7.62mm projectile has a liquid phase sintered tungsten alloy (LPS) core. The tungsten is alloyed with nickel and iron and is not magnetic. Liquid phase sintered tungsten alloy cores are true KE penetrator technology; very effective at penetrating hard armors. Total weight of the M1158 7.62mm projectile is 9.8 g, or about 151 grains. None of these projectiles have been sold on the civilian market, but they would be very difficult to distinguish from M80 7.62mm projectiles.