FN America AR-15 5.56x45mm NATO 14.70in M4 Profile Carbine Length Gas System Black Phosphate Cold Hammer Forged Chrome Lined. After forging each barrel is Magnetic Particle tested to ensure that it is free of microstresses or flaws resulting in consistency and quality in every barrel shipped from the factory. The bore and chamber are chrome lined to help resist corrosion and provide resistance to heat erosion which greatly improves barrel life and reliable chambering / extraction. The M4 style feed ramps and barrel extension provide consistent feeding and the matte black Manganese Phosphate finish resists external corrosion and oxidation Specifications for FN America AR-15 5.56x45mm NATO 14.70in Threaded Barrel: Manufacturer: FN America Color: Manganese Phosphate Additional Features: Chrome-Lined Carbine Length Length: 14.7 in Package Contents: FN America AR-15 5.56x45mm NATO 14.70in Threaded Barrel FN 20-100405 AR-15 5.56x45mm NATO 14.70 M4 Profile Carbine Length Gas System