Specter Black Diamond Carbine Complete Upper 5.56mm NATO 16 Inch Barrel 1:7 Inch Twist Rate. Forearm bridges the gap between the upper receiver and handguard and is marked for position on all four sides. Forged 7075-T6 aluminum YHM flat top upper receiver, T-marked. Forward assist. Sixteen inch 4140 steel, diamond fluted barrel, heat treated to RC 25-32. Chambered in 5.56 NATO and chrome-lined. Phantom 5C2 flash hider/compensator. Specter length Diamond handguard. Forearm endcap. Low profile gas block. Forearm mounted flip front sight. Flip rear sight. Total weight 4.8 pounds. Made in the USA.