Upper receiver group for AR-15 firearms manufactured by Daniel Defense. The MK18 upper receiver is modeled after the Close Quarters Battle Receiver developed by the US Navy and later used by various United States Special Operations groups. The receiver features a chrome-lined barrel for improved heat resistance and comes equipped with Daniel Defense's legendary RIS II quadrail handguard. This complete upper receiver group comes included with an M16 profile bolt carrier group and is compatible with all mil-spec lower receiver groups.