The mag release button had a horizontal line pattern on it, versus the round line pattern identified on The existing ones, see the image down below for an instance: Certainly, I'm certain the upper receiver is Colt, combined with the BCG. It is actually the barrel that may be questionable https://spencerwtybi.wikiworldstock.com/1082443/not_known_facts_about_colt_combat_unit_rail_gun_45