Premiere Manufacturing Complete AR15 BCG 5.56 / .223 - Polished Black Nitride The best BCGs for replacement parts and builds have strong and dependable carriers with trusty bolt assemblies that cycle reliably. That's exactly what you'll get with this high quality complete BCG. Premiere Manf M16 bolt carrier groups are polished before and after the H&M BLACKNITRIDE+™ process, producing a beautiful finish and reducing the friction coefficent. The carrier is made from 8620 steel. The bolt is made from 9310 steel. The 223 Bolt and Bolt Carrier Assembly is compatible with 5.56 NATO and 300 Blackout. Enhanced 9310 Steel (Bolt) 8620 Tool Steel (Carrier) Mil-Spec Extractor Spring, black extractor insert, Viton O-Ring Tool Steel Extractor Shrouded Firing Pin Mil-Spec Gas Key (4130 Steel) attached with Grade 8 hardware and heavily staked Caliber: .223 / 5.56 / 300 Blackout Bolt is shot Peened and MPI All BCG components pre-polished before being processed and then post polished! SKU: A00348 UPC: 860006521989