Complete BCM Rifles, Carbines, and AR Pistols, include: 1 Magazine, Cable Lock, USGI Manual, and FET.Featuring BCM's Patent Pending MK2 Upper ReceiverThis proprietary design offers enhanced rigidity over the USGI product. The increased rigidity limits barrel deflection which aids in consistency/accuracy. Less flex also reduces premature damage, wear, and failure of bolt lugs from misalignment. A gas expansion chamber is machined above the charging handle track, combined with dual vents machined at the rear (each side, above charging handle latch) help to redirect and vent gas away the shooters face.