CMMG M4 Profile Uppers have the following standard features. * Mil-spec certified 4150 chrome-moly vanadium steel M4 contour barrel * 5.56x45 NATO chamber * 1/9 twist * Hard chrome lined chamber and bore * M4 feed ramps * 11 degree recessed target crown * F marked forged front sight base * Parkerized Barrel including under the front sight base * A2 Flash hider installed with Peel washer * Forged A3 upper receivers are T marked and have extended feed ramp cuts (M4 ramps). * Semi Auto bolt carrier Each barrel is individually magnetic particle tested. Barrels are engraved CMMG MPC 5.56 NATO 1/9. Each Upper is head spaced and test fired before shipping. Upper specific features are listed with the individual item. When selecting the gas piston operating system, it will override your choices for the bolt carrier and front sight/gas block.