Proof Research makes their steel barrels in-house with the exact same commitment to quality and repeatability as employ on their carbon fiber barrels. The drilling, rifling, and lapping process is identical to their composite barrels. They start with the same steel as they use in the carbon fiber barrels. It is a double stress-relieved 416R stainless steel, a pre-hardened chromium stainless steel that was specifically designed by engineers in collaboration with rifle barrel makers to provide the consistent, high quality and durability the firearms industry demands.