According to only one article that I've seen, some states currently make it a felony to possess armor piercing pistol ammo. No grandfathering in. I'll just put this here.
"...Arguably the most disturbing part of the proposal is ATF’s dedication to implementing the new rule and associated disregard for the state-level ramifications of such a ruling. At this time, as many as twelve states (Alabama, California, Connecticut, Indiana, New Hampshire, New Jersey, New York, Michigan, Mississippi, Oklahoma, Tennessee, and Texas) explicitly forbid the possession of armor piercing ammunition. In several of these, possession constitutes a felony. Simply put, the proposal would instantly turn thousands of peaceable gun owners into felons simply because ATF chose to arbitrarily reclassify one of the most popular 5.56mm cartridges on the market. The consequences of such an action could be quite severe, but at minimum, thousands of gun owners will have sufficient standing to bring the agency to court...."
Oklahoma bans the possession, carrying, use, attempted use, manufacture, importation, advertising for sale or sale of any “restricted bullet.” A “restricted bullet” is a round or elongated missile with a core of less than 60% lead and that has a fluorocarbon coating, designed to travel at high velocity and capable of penetrating body armor. M855 does not meet that definition.
See (https://www.ok.gov/osbi/documents/SDA_Lawbook_NOV_2013.pdf) page 33.