Radical Firearms Complete Upper Assembly, 300 Blackout, 16 Barrel, 1:8 Twist, Black, MLOK Handguard, A2 Flash Hider RF00375 The Radical Firearms 300 Blackout upper is a complete MIL-STD upper ready to drop on any MIL-STD lower Receiver. Perfect for the novice or advanced shooter wanting to finish out that build and hit the range. No matter what your style of shooting is" Radical Firearms has you covered.