16" M4 Profile Barrel 5.56 .223 for AR-15 (Carbine) This 5.56 chambered 16" M4 Profile Barrel is machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish and QPQ coated M4 feed ramp extension. Quench Polish Quench (QPQ) is a specialized type of nitrocarburizing case hardening that increases corrosion resistance. It is sometimes known by the brand name of Tufftride, Tenifer Black Nitride or Melonite. QPQ is a huge improvement over Chrome Lined barrels. Unlike chrome lining, where the chrome is built up on the surface, QPQ converts the surface without the risk of dimensional build up. Length - 16" Material - 4150 Chrome Moly Vanadium 11-Degree Target Crown - Further improve accuracy Profile - M4 Finish - QPQ Corrosion Resistant Gas System Length - Carbine Gas Block Journal - .750" Gas Block Journal Twist Rate - 1/7 Twist Muzzle - 1/2x28 Threaded Weight - 28oz SKU: KM55616M4 UPC: 860006522037