Colt Verified Proof V&P In triangle marking on still left side of your barrel among the legs of your entrance sight base: 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 barrels, https://coltcombatunitrailgun4533421.blogolenta.com/28147762/colt-m16a1-for-sale-things-to-know-before-you-buy