.458 SOCOM/.450 Bushmaster bolt carrier groups (BCGs) are Magnetic Particle Inspected (MPI) to ensure high performance. BCA's .458/.450 BCG is made with durable 9310 Steel and compatible with both 450 Bushmaster and .458 SOCOM uppers; the gas key is also staked from the side for enhanced durability. Includes Bolt, Bolt Carrier, Extractor Pin, Firing Pin, and Cam Pin.