The FN AR-15 Barrel (brand part no. 36421) is a 16-inch, 5.56x45mm NATO carbine-length barrel that FN America builds using the same hammer-forging process behind its military machine gun barrels. Each barrel is forged from high-grade chrome-moly-vanadium steel to the same forging and quality standards FN uses for its full-auto military contracts, then Magnetic Particle tested 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, which extends barrel life and keeps chambering and extraction reliable round after round. An M4-pattern barrel extension and matching feed ramps keep feeding consistent, and the matte black Manganese Phosphate finish protects the exterior from corrosion and oxidation. It’s a durable, mil-spec-grade barrel upgrade for AR-15 builders who want proven reliability over a budget option.

Key Specifications

• Chambered in 5.56x45mm NATO for standard AR-15 platforms.
• Measures 16 inches in length with a carbine-length gas system.
• Rifling uses a 1:7 twist rate, stabilizing heavier 5.56 bullet weights.
• Cold hammer forged from chrome-moly-vanadium steel to the same standard FN uses on its military-contract barrels.
• The bore is chrome lined for corrosion resistance and extended barrel life under sustained use.
• The chamber is chrome lined as well, improving reliable chambering and extraction.
• Every barrel is Magnetic Particle tested to confirm it’s free of microstresses or flaws before shipping.
• Machined with an M4-pattern barrel extension for a direct, mil-spec fit.
• Cut with M4-pattern feed ramps for consistent feeding.
• Finished in matte black Manganese Phosphate for external corrosion and oxidation resistance.

Frequently Asked Questions

What gas system does this barrel use? It’s set up for a carbine-length gas system, matching the standard 16-inch AR-15 carbine configuration.

Why chrome line the bore and chamber? Chrome lining resists heat erosion and corrosion, which extends the barrel’s service life and keeps chambering and extraction reliable through heavy round counts.

Is this barrel rated for sustained rapid fire? It’s forged to the same standard FN uses for its military machine gun barrels, giving it strong heat tolerance, though any semi-auto barrel benefits from managing cyclic rate on extended strings.

Buy the FN AR-15 16-inch 5.56 NATO Barrel, Black Phosphate, Carbine Gas

Build your AR-15 around a barrel forged to the same standard as FN’s military contracts. Order it through our FN America lineup of AR barrels from our Lubbock, Texas gun shop.