FN 20-100042 AR-15 5.56x45mm NATO 18" Button Rifled M16 Profile Rifle Length Barrel - Chrome Lined

The FN 20-100042 is a factory FN AR-15 replacement barrel chambered in 5.56x45mm NATO. This genuine 18" barrel is cut on the classic M16 profile and finished in matte black Manganese Phosphate for excellent resistance to external corrosion and oxidation.

The bore is cold hammer forged from steel and button rifled for consistent, uniform geometry, then chrome lined for extended service life and easier cleaning under hard use. A rifle length gas system is specified, and the barrel is fitted with M4-style feed ramps and a barrel extension to promote reliable feeding from the magazine into the chamber.

Built as a direct-fit replacement for an existing AR-15 upper assembly, this FN barrel brings factory-spec quality to a custom build, a parts refresh, or a worn-out replacement.