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-spec compliant 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. 16" HBAR Barrel and A2 Flash Hider. Our free-float handguard: RPR keeps your hands cool and provides plenty of room for M-LOK accessories. Complete upper including Bolt Carrier Group and Charging Handle.