This CMMG bolt carrier group is built for AR-15 uppers chambered in 6.5 Grendel and 6mm ARC, two cartridges that share a common Type II bolt face. It ships fully assembled and ready to run in a matching upper. The bolt is 9310 steel, the carrier is chrome-lined 8620, and the extractor is 4140, with a phosphate finish. The carrier uses the AR-15 pattern, so it drops into a standard AR-15 upper receiver once the barrel matches. Features: Complete AR-15-pattern bolt carrier group Chambered for 6.5 Grendel / 6mm ARC (Type II bolt face) 9310 steel bolt 8620 carrier, chrome-lined 4140 extractor Phosphate finish Fully assembled This is a Type II bolt face, NOT a 5.56 BCG. Pair it only with a 6.5 Grendel or 6mm ARC barrel, and run magazines made for those cartridges. Have a gunsmith check headspace with the correct gauges before you fire it.