Comes with a magpul p mag from what I heard from the ffl so I think it's model b (not 100% which is which though)Did you get the AR-10B or the AR-10A? You will need to know that when you go to buy extra mags. Also make sure that when you buy parts for it (except the trigger) that they are for the Armalite AR-10 version and not the DPMS pattern.