A Short while ago I have found A number of uppers which might be choose offs from rebuilt M16A1 rifles staying sold as "new substitution uppers". The "C" about the barrel would point out a chrome chamber only barrel. But AFAIK, Colt marked the "C" up near the muzzle on https://gregorytcjmn.wikijm.com/1080883/the_greatest_guide_to_colt_m16a1_for_sale