Build the custom rifle you want without shooting holes in your budget. The Anderson Manufacturing 16 M4 Complete Upper has a forged build featuring a 16 M4 contour barrel with 1:8 rate-of-twist rifling and Knight Stalker flash hider. Comes with M16 Bolt Carrier Group and standard charging handle. Carbine-length EXT forearm. .750 standard-carbine gas block. Caliber: 5.56 NATO. Type: AR-15 Uppers.