AR15-A4 Lightweight LE Carbine 5.56mm Caliber 16.5 Inch Barrel 20 Rounds Comes standard with an optics ready rail and MaTech flip-up rear iron sight which has adjustment for both windage and elevation. The 16.5 inch standard weight barrel and bolt are magnetic particle tested after proofing by Colt to ensure they are made of perfect steel with zero flaws. 1:7 inch twist gives the barrel flexibility to use a wide range of ammunition from 40 grain varmint rounds to 77 grain long range match. New roll mark of AR-15A4 recognizes Colt's newest designation of an optics ready carbine. Comes with two Magpul 20 round magazines.