Quite a few rifles were being rebuilt, especially Vietnam era rifles. Usually the barrels were being changed. Some examples of markings identified on replacment barrels incorporate: Sad to say, I am on travel so I can't post photographs with the bolt. It really is MPC engraved. The only real marking https://colt-m16a1-for-sale92344.dgbloggers.com/31599587/colt-python-6-for-sale-for-dummies