CMMG MK4 5.56x45MM NATO ASSEMBLED UPPER RECEIVER W/PINNED & WELDED MUZZLE BRAKE The carbine upper that keeps it simple. Chambered in 5.56x45mm, this RESOLUTE upper group's 14.5" barrel comes with the ZEROED SVD muzzle brake pinned & welded to the muzzle. This is the perfect choice when you want to go as short as possible while still meeting overall length requirements for rifle barrels, so no NFA rules or SBR registration. This upper group does NOT include BCG or charging handle. FEATURES Platform: Mk4 Caliber: 5.56x45mm Operating System: Direct Impingement Barrel Length: 14.5" Barrel Twis Mfg: Cmmg