Brownells Brn-4 5.56X45 13.7'' Medium Chrome Lined Barrel, Phosphate

The Brownells BRN-4 5.56x45 13.7" medium chrome-lined barrel is purpose-built for HK 416-compatible AR platform rifles, offering shooters a hard-to-find component that bridges classic 416 ergonomics with modern build flexibility. Machined by Faxon and engineered specifically for early-generation HK 416 upper receivers, this barrel delivers the rigidity and precision you'd expect from a battle-proven design without the typical weight penalty of heavier profiles. The medium contour strikes a practical balance—it maintains the barrel stiffness needed for accuracy while keeping your overall rifle weight and handling responsive, making it equally at home on a carbine or a tighter tactical build.

Chrome lining on the bore and chamber resists corrosion and extends barrel life under high round counts, a feature especially valued by shooters running hot ammunition or running drills frequently. The phosphate finish provides a durable, low-gloss exterior that's easy to maintain in the field. Button rifling with a 1:7 twist rate stabilizes a wide range of 5.56x45 NATO and .223 Remington loads, so you're not locked into boutique ammunition. The 1/2"x28 muzzle threads are standard across the industry, giving you unlimited options for suppressors, flash hiders, or compensators without adapter hunting.

Installation is straightforward with the Brownells barrel nut (not included) and requires matching the correct BRN-4 gas block to your barrel length. All BRN-4 barrels share the same piston rod assembly, simplifying parts decisions downstream. This 13.7" length lands in the short-to-medium carbine range, balancing velocity and handling for both defensive and hunting-oriented builds.

Key Features

• Medium contour profile balances accuracy and weight for handy, responsive handling
• Chrome-lined bore and chamber resist corrosion and wear under sustained fire
• Phosphate finish for durability and easy field maintenance
• Button rifled, 1:7 twist—stabilizes 5.56 and .223 Remington across velocity ranges
• 1/2"x28 muzzle threads for universal muzzle device compatibility
• Engineered for early HK 416 upper receivers and the full BRN-4 parts ecosystem
• 13.7" length optimized for carbine-length gas systems

Specifications

Frequently Asked Questions

Will this barrel work on a standard AR-15 upper receiver?

No. The BRN-4 barrel is specifically designed for early HK 416 upper receivers and the Brownells BRN-4 parts ecosystem. It uses the extended barrel extension common to 416-pattern builds and requires the BRN-4 barrel nut for proper fitment.

What gas block do I need for this barrel?

You'll need a BRN-4 gas block matched to your barrel length. All BRN-4 barrels share the same piston rod assembly, so the gas block selection depends on whether you're running a carbine or rifle-length system for your specific barrel. Consult the BRN-4 parts lineup to confirm the correct model for 13.7" length.

Can I shoot .223 Remington in this barrel?

Yes. The 5.56x45 chamber accepts both 5.56 NATO and .223 Remington ammunition, giving you flexibility with commercial ammunition supplies.

What's included in the box?

The barrel only. You'll need to source the BRN-4 barrel nut, the appropriate BRN-4 gas block for your build, and gas block coil pins separately to complete your upper assembly.