ITS Tactical discusses why the Steel Penetrator Tip of the M855/SS109 5.56x45mm NATO round does not make it legally a Armor Piercing (AP) round.
Bryan writes …
Throughout my time in the Military, I’d always referred to M855/SS109 5.56 Ammunition (Green Tip) as armor piercing rounds or AP. For the life of me I can’t recall where I first heard that mentioned, but it was fairly common for it to be referred to as that.