CMMG M4 Upper,14.7 in. Permanent Birdcage Flash Hider New 14.7" M4 upper w/permanent hider. Permanent hider brings overall barrel length to legal 16”. This upper comes with M4 handguards and is complete with bolt, carrier and charging handle. CMMG semi auto bolt carriers have the shrouded firing pin to protect against hammer wear. Upper receivers are "T" marked and include extended feed ramp cuts. Features include standard contour M4 barrel, notched M4 handguard cap, chrome-lined 5.56mm chamber and bore, 1/7 twist, parkerizing under “F” marked forged front sight base and magnetic particle testing on every barrel. When ordering with optional gas block, barrels will not be drilled for taper pins. Barrel is marked CMMG MPC 5.56 NATO 1/7.