Upper Receiver assemblies complete with barrel, gas block and handguard installed. These upper receivers feature 416R stainless steel barrels, with either a 1-9 twist or 1-8 twist in the 20" and 24" bull barrels, and are chambered in 5.56mm. Barrel extensions and upper receiver include M4 feedramps. Upper receiver is forged 7075-T6 aluminum and has T-Marks. M4 and 7.5" models feature stainless steel A2 flash hiders, 1/2-28 threads, modular handguard compatible with Magpul rails and .750" gas blocks. Bull barrel models feature either a 16", 20" or 24" barrel. These models also include a tubular style handguard with a .936" gas block. All upper receivers do not include a charging handle or bolt carrier group.All NFA Rules apply.