CMMG, Bolt Carrier Group, AR-15 Complete Mil-Spec M16 bolt carrier group for 5.56mm/.223 and 300 BLK. Bolt: 9310 Steel, Phosphate Finish Carrier: 8620 Steel, Chrome Lined, Phosphate Finish Extractor: 4140 Steel, Phosphate Finish All CMMG products come with our Lifetime Quality Guarantee.