TacFire's 300 BO unassembeld pistol build kit includes: 7.5" parkerized barrel with pistol gas system (USA made); 5.56/300 BO NATO bolt carrier group (USA made); 7" Ultra Slim KeyMod free-float handguard with detachable rails; Lower parts kit included with trigger and hammer (USA made); .750 gas block; pistol length gas tube; standard receiver end plate; Mil-Spec/Commercial castle nut; Mil-Spec buffer tube; 3 oz buffer; buffer tube spring; Mil-Spec charging handle; dust cover; forward assist; 5/8"-24 thread bird cage A2 muzzle brake; pistol grip (USA made) and upper receiver 5.56/223/300BO with M feed ramps (USA made).