I have RIA drawings specifing barrel markings on a fresh USGI rifle and that marking is just not approved. Sad to say, I'm on journey so I can't publish images of the bolt. It is actually MPC engraved. The sole marking on the carrier is definitely the "C" stamp about https://spencerwtybi.wikiworldstock.com/1082443/not_known_facts_about_colt_combat_unit_rail_gun_45