FN AR-15 barrels are hammer forged using the same proprietary high grade Chrome Moly Venadium steel used in FN's venerable machine gun barrels produced to handle the punishment of sustained fully automatic fire. 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.