I have a A1 upper that has P and M on the left side at the rear part of the handle. The barrel and sight is parked and the aged parked od look. I only found a marking on barrel i think GG or G stamped twice and maybe a c or something but its done after the park so it could be anything somerone else done. Its post be a 1/7 twist HB,it has fineline grooves in barrel and not as noticeable  and feel like the colt ones made in the 90's. Upper is black and somewhat pitted under finish. It does not have the sp1 rear sight wheel but it has a knob sorta like the a2 but setup as a A sight. I looked under handguard before but will look again and don't remember it been marked under it. It does not have nato 5.56 or anything marked on barrel.