This BCA AR-15 complete 6.5 Grendel rifle length upper has an 18″ heavy barrel with a 416R stainless steel finish, and features a 1:8 twist rate, with a mid-length gas system. It includes a 15″ MLOK rail, an M4 flat-top billet upper receiver, a BCA bolt carrier group, a flash hider, and a gen 2 right charging handle(patent pending). This 6.5 Grendel upper is compatible with any mil-spec AR-15 lower.