Quoted: With this display seize within the SAS vid, the pivot pin boss certain looks reprofiled to me. The two radii are actually Minimize The "C" within the barrel would point out a chrome chamber only barrel. But AFAIK, Colt marked the "C" up near the muzzle on their own https://ezmarkbookmarks.com/story18597199/colt-m16a1-for-sale-things-to-know-before-you-buy