The DPMS AR-15 A3 Lightweight Flattop Upper Assembly is a drop-in part that will attach to virtually any standard AR-15 lower assembly. Comes complete with charging handle, Commercial bolt and bolt carrier assembly, it is ready to pin to a complete lower assembly with no modification. The DPMS Lightweight upper comes with carbine length GlacierGuard handguards that utilize 15 internal fins, rather than the standard aluminum double-shield, for heat dispersion. These unique fins, while dispersing the heat generated by rifle fire, also provide unsurpassed strength and rigidity for the handguard. Barrel is a lightweight profile that saves weight without sacrificing accuracy and the versatile 1 in 9" twist allows for a wide range of projectile weights. Upper Receiver Type: A3 Flat-Top Barrel Length: 16" Barrel Contour: Light Contour Barrel Material: Chrome Moly Steel Muzzle Thread Pattern: 1/2"-28 Chrome Lined: No Barrel Finish: Black Matte Twist Rate: 1 in 9" Chamber: 5.56x45 NATO M4 Feed Ramps: Yes Muzzle Device: A2 Flash Hider Gas System Length: Carbine Gas Block Diameter: .750" Handguard: GlacierGuard Sights: A2 Front Sight Bolt Carrier Assembly Included: Yes Bolt Carrier Type: Commercial