There is no AP ammo ban. You can buy .50 BMG AP, API and APIT if you want (when it’s available.) I’ve bought all three this year.
"Armor Piercing Ammunition" (a technical, legal term) is banned. See the definition of "Armor Piercing Ammunition" in US code: Title 18, 921 (17).
The manufacture and sale and use in a crime of violence of Armor Piercing Ammunition is prohibited.
I think the provision for determining "sporting purposes" allows BATF to exempt .223 from the APAmmo ban.
Note in the definitions that "Armor Piercing Ammunition" is handgun ammo. Rifle ammo, no matter how much hardened steel it can penetrate, is not "Armor Piercing Ammunition". By definition.
IANAL
As explained above, the ban only applies to handgun ammunition. Dumb I know, but it was thought up by the likes of Chuckie Schummer, and Diane Frankenstein, so what do expect?