FN 36423 AR-155.56x45mm NATO 18" Rifle Length Gas System, Black Phosphate Cold Hammer Forged Chrome Lined

The FN 36423 is a cold hammer forged AR-15 barrel in 5.56x45mm NATO with an 18-inch rifle length gas system, purpose-built for shooters who demand accuracy and longevity from their platform rifle. FN's century-plus legacy in barrel manufacturing translates directly into this component: each barrel is forged from high-grade Chrome Moly Vanadium steel using the same proprietary process that hardens FN's machine gun barrels. The result is a tube engineered to handle sustained fire without compromise.

Chrome lining inside the bore and chamber resists corrosion and heat erosion—two of the primary culprits behind accuracy fade and reliability issues on high-round-count builds. The black phosphate exterior finish mirrors that durability; it's designed to resist oxidation and surface corrosion in field conditions. M4-style feed ramps and an integral barrel extension ensure the kind of feeding consistency that separates a rifle you trust from one that leaves you troubleshooting at the range. Before it ships, every barrel undergoes magnetic particle inspection to catch internal flaws or stress risers that could compromise performance downrange.

The 18-inch rifle length gas system strikes a balance between velocity and ergonomics—you'll get full burn from rifle-length tuning while keeping overall length manageable for most applications. The gas block interface measures .750 at the journal, a standard specification that works with common AR-15 tuning components. Whether you're building a precision rifle, a duty-inspired carbine, or a hard-use field gun, this barrel gives you the FN quality standard without the custom-build markup.

Key Features

• Cold hammer forged from Chrome Moly Vanadium steel for superior durability and consistency
• Chrome lined bore and chamber resist corrosion and heat erosion for extended barrel life
• Magnetic particle tested to eliminate internal stress and flaws before delivery
• M4-style feed ramps for reliable ammunition feeding
• Black phosphate finish protects against external corrosion and oxidation
• .750 gas block journal for standard AR-15 component compatibility

Specifications

Frequently Asked Questions

What gas system length is this barrel?

This is a rifle length gas system, the longest standard AR-15 gas port configuration. Rifle length systems typically offer softer recoil impulse and are often preferred on precision or duty-focused builds.

Is the barrel chrome lined?

Yes. The bore and chamber are chrome lined to resist corrosion, heat erosion, and the wear that comes with sustained fire. Chrome lining is particularly valuable if you plan to run high round counts or store the rifle in humid conditions.

What does the .750 gas block journal mean?

The gas block attaches at a .750-inch diameter journal. This is the standard specification for most AR-15 gas blocks, so you'll have a wide range of tuning and brake options available from common manufacturers.

Is this barrel suitable for long-range or precision shooting?

This barrel is manufactured to FN's cold hammer forging standards with magnetic particle inspection for consistency—the same process used in FN's professional and military applications. While individual rifle accuracy depends on the complete build, this barrel provides the kind of manufacturing precision and durability you'd want in any precision or long-range platform.