The FN AR-15 Barrel (brand part number 36423) is an 18-inch barrel chambered in 5.56x45mm NATO with a rifle-length gas system, built for shooters who want the added velocity and sight radius of a longer-barreled AR-15. FN hammer-forges the barrel using the same proprietary high-grade chrome-moly-vanadium steel used in the company’s machine gun barrels, which are built to handle sustained full-automatic fire, then Magnetic Particle tests every barrel to confirm it’s free of microstresses or flaws before it ships. The bore and chamber are chrome-lined to resist corrosion and heat erosion, extending barrel life and keeping chambering and extraction reliable, while M4-style feed ramps and a matte black manganese phosphate finish round out the build.

Key Specifications

• Chambered in 5.56x45mm NATO.
• Measures 18 inches with a rifle-length gas system.
• Cut with a 1:7 twist rate.
• Cold hammer forged from chrome-moly-vanadium steel.
• Bore and chamber are chrome-lined for corrosion and heat-erosion resistance.
• Built with M4-style feed ramps and barrel extension for reliable feeding.
• Finished in matte black manganese phosphate.
• Every barrel is Magnetic Particle tested for defects.

Frequently Asked Questions

What gas system does this barrel use? A rifle-length gas system, matched to the 18-inch length.

Is this barrel chrome-lined? Yes, both the bore and chamber are chrome-lined for corrosion resistance and extended service life.

Buy the FN 18-Inch AR-15 Barrel

Get extra velocity and sight radius with an 18-inch, chrome-lined barrel. Order it from our FN America lineup of AR barrels for fast, reliable shipping from our Lubbock, Texas gun shop.