Colt Confirmed Proof V&P in triangle marking on left side with the barrel concerning the legs of the entrance sight base: The "C" around the barrel would indicate a chrome chamber only barrel. But AFAIK, Colt marked the "C" up close to the muzzle on their early barrels, not underneath https://troyabzwt.wikififfi.com/1079110/the_greatest_guide_to_colt_m16a1_for_sale