AR-15 .223/5.56 NATO/.300 Blackout/.350 Legend Rear Charging AR-15 Bolt Carrier Group Shoot a huge range of calibers with this bolt carrier group (BCG) compatible with Rear Charging 5.56, 223, 300 Blackout, and 350 Legend AR-15 uppers or rifles. BCG are Magnetic Particle Inspected (MPI) to ensure high performance. BCG is made with durable 9310 Steel and the gas key is also staked from the side for enhanced durability. Caliber / Gauge: .223/5.56 NATO/.300 Blackout/.350 Legend Carrier Style: Standard Platform: AR-15 Bolt Finish: Parkerized Bolt Material: 9310 Steel Carrier Finish: Black Nitride Gas Key: Staked from the side to increase longevity Magnetic Particle Inspection