"... with the popularity of AR-15 pistols, the ATF has cracked down on certain .223 Remington bullets – for example, copper bullets. This is because a copper bullet for a .223 Remington cartridge is now “armor piercing” in the eyes of the ATF because it can be used in a handgun."
^^ is there a cite for this?
Also on a Federal level, the ATF has clarified recently that civilians can own/possess/use AP ammo. The restrictions are placed on the FFL.