Genuine USGI Production, NOT inferior commercial grade. We've seen just about everything out there & this is the finest BCG made. Legal and recommended in AR-15s. SPECS - 158 Carpenter Steel HPT/MPI Marked Bolt - 8620 Steel Carrier (Chrome Lined) - Properly Staked Gas Key (Chrome Lined) - HD Extractor Spring Assembly with Rubber O-Ring Enhancer Why do others substitute other inferior/untested steels? To decrease the cost of the part. Carpenter 158 is a high technology steel that is very expensive and can only be ordered in 20,000 lb mill runs. It is the only steel allowed by the US (and Foreign) Militarys for the very demanding needs of this high stress, critical part. *BARRELS & BOLTS MUST BE PROPERLY CHECKED FOR HEADSPACE PRIOR TO USE. FAILURE TO DO SO MAY RESULT IN FIREARM DAMAGE, PERSONAL INJURY, OR DEATH*