The Radical Firearms M4 Upper Receiver is a flat top, law-enforcement grade, drop in receiver, ready to be mounted to any Mil-Spec AR-15 lower receiver! This fully MIL-STD receiver provides a high-quality upper for any level budget or shooter. Comes complete and assembled with Upper Receiver, Forward Assist, Ejection Port Door, RF Barrel Nut. 20″ 6.5 Grendel Complete Upper comes with a Stainless Steel Barrel and Pepper Pot Brake. Our free-float handguard. This is a complete upper including Bolt Carrier Group and Charging Handle.