I've RIA drawings specifing barrel markings on a whole new USGI rifle Which marking is just not approved. The "C" within the barrel would reveal a chrome chamber only barrel. But AFAIK, Colt marked the "C" up close to the muzzle on their own early barrels, not beneath the handguards. https://bookmarkshq.com/story19975182/a-review-of-colt-python-6-for-sale