Townhall and others report that M855 “Green Tip” may already be classified as armour piercing by the BATFE …

When you take a look at the 2005 ATF Regulation Guide, you’ll see an exemption for AR-15 “green-tip” ammunition, which means it exempted from the definition of “armor piercing” and therefore is legal on the federal level.

 

…

When you look at the last page of the new, most recent ATF 2014 Regulation Guide, which was published in January, there is no longer an exemption for AR-15 “green-tip” ammunition.

You can still buy it online. Take a look at IronSights for a list of retailers still stocking the round.

Thanks to HK and others who sent this in.