Drop On (MIL Spec) Upper Receiver Assembly that upgrades your AR15/M16/M4 type lower receivers or rifles. 5.56 x 45mm NATO 16.25" or 12.5" Quick Change Barrel 1:7" RHT, A 1/2"28 TPI & Chrome Lined Barrel Short Stroke Gas Piston Operation Dual Feed Accepts ALL AR15/M16 Magazines & M27 Linked Ammunition Precision Machined 7075 T6 Billet Upper Receiver, Feed Cover and Charging Handle Precision Machined Billet Steel Feed Tray Finish: Manganese Phosphate & Type III, Class 2 Hardcoat anodize Black for Maximum Corrosion and Wear Resistance Dry Film Lubricant Applied to Critical High Friction Surfaces Mfg: Fightlite Industries