Lately I Have noticed A number of uppers that are consider offs from rebuilt M16A1 rifles currently being sold as "new alternative uppers". The "C" about the barrel would point out a chrome chamber only barrel. But AFAIK, Colt marked the "C" up close to the muzzle on their early https://shanevxxwu.shivawiki.com/6977871/colt_m16a1_for_sale_fundamentals_explained