The FN Barrel AR-15 5.56 NATO 16" M4 Contour is a genuine mil-spec replacement barrel built for shooters who demand the reliability FN brings to military and law enforcement duty weapons. This 16-inch carbine-length barrel pairs the proven M4 profile with a 1:7 twist rate, making it equally at home for defensive shooting, duty use, or general-purpose AR builds where a shorter, handier package matters. FN manufactures these barrels from U.S. sourced Chrome Moly Vanadium per Mil-B-11595E specifications, then subjects every piece to High Pressure Testing (HPT) and Magnetic Particle Inspection (MPI) to catch micro-stresses and hidden flaws before they ship. That quality control translates to consistent chamber headspace and reliable feeding and extraction across thousands of rounds.

The bore and chamber are chrome lined—a feature that extends barrel life by resisting heat erosion and corrosion, especially valuable if you shoot hot loads or plan to run significant round counts. The exterior matte finish is Manganese Phosphate, a military-grade coating that guards against external rust and oxidation without the slip of a slick finish. The M4-style feed ramps are cut into the barrel extension itself, supporting the kind of reliable feeding you expect from a combat-proven design. If you're replacing a worn tube, building a clone rifle, or simply want a barrel with genuine mil-spec pedigree backing it, this FN tube delivers the fit and finish serious shooters recognize.

This is a barrel only—not a complete upper receiver assembly—so you'll be pairing it with your own bolt carrier group, handguard, upper receiver, and gas tube or system to complete your build. Carbine-length gas systems are the standard for 16-inch AR builds and offer a balance between reliability and ergonomics that's hard to beat for most shooters.

Key Features

• 16-inch M4 contour carbine-length barrel in 5.56 NATO
• 1:7 twist rate suitable for standard to heavier 5.56 rounds
• Chrome-lined bore and chamber for extended barrel life and corrosion resistance
• Chrome Moly Vanadium steel construction per military specifications
• High Pressure Tested (HPT) and Magnetic Particle Inspected (MPI) for consistency
• M4-style feed ramps integrated into barrel extension
• Manganese Phosphate matte finish resists external corrosion and oxidation
• U.S. sourced materials and manufacture

Specifications

Caliber	5.56 NATO
Barrel Length	16 inches
Contour	M4
Gas System Length	Carbine
Twist Rate	1:7
Material	Chrome Moly Vanadium (Mil-B-11595E)
Chamber Lining	Chrome lined
Bore Lining	Chrome lined
Finish	Manganese Phosphate matte
Feed Ramps	M4-style
Quality Control	HPT and MPI tested

Frequently Asked Questions

What twist rate is this barrel and what ammunition does it handle?

The FN 16" barrel features a 1:7 twist, which is the standard mil-spec rate for 5.56 NATO. This twist will stabilize the full range of common 5.56 rounds, from lighter 55-grain loads through heavier ammunition, making it versatile for most shooters and shooting disciplines.

Is this barrel complete, or do I need other parts to use it?

This is a barrel only. You'll need to pair it with an upper receiver, bolt carrier group, charging handle, handguard, and gas system components (gas tube, block, or rail) to build a complete upper assembly. It does not include those parts.

What does chrome lining do and why does it matter?

Chrome lining on both the bore and chamber extends barrel life by resisting heat erosion and corrosion. This improves durability under high-round-count shooting and helps maintain reliable chamber dimensions and extraction over time—particularly valuable if you shoot frequently or in harsh conditions.

What gas system length does this carbine-length barrel use?

The barrel is configured for a carbine-length gas system, which is the standard for 16-inch AR-15 builds. Your gas tube, block, or piston system should be carbine-length to match.