Brownells Brn-4 5.56X45 Nato 10.4'' Heavy Chrome Lined Barrel Phosphate

The Brownells BRN-4 5.56x45 NATO 10.4" heavy barrel is a short-stroke piston rifle component engineered for early HK 416 upper receivers and the complete BRN-4 platform. Machined by Faxon and finished with a hard-wearing deep black phosphate coating both inside and out, this barrel delivers the rigidity and reliability you need in a compact package. Whether you're building a duty-inspired modern rifle, an integrally-piston 5.56 platform, or a short-barreled setup, the BRN-4 heavy profile emphasizes barrel stiffness over weight—trading the ounces for the mechanical advantage of minimal flex under pressure.

The 10.4-inch length positions this barrel for close-quarters performance and maneuverability while maintaining enough velocity for rifle-round ballistics at practical distances. It's chambered in 5.56x45 NATO, which means you can run both commercial NATO spec and .223 Remington ammunition without worry. The barrel features a 1:7 rate of twist and a ½-28 muzzle thread pitch, giving you broad compatibility with suppressors, flash hiders, brakes, and other muzzle devices in the standard aftermarket ecosystem. The extended barrel extension provides robust interface contact with early HK 416 uppers and simplifies installation with the BRN-4-specific barrel nut.

As part of the BRN-4 family, this barrel pairs with Brownells' matched bolt carrier group and gas block system. All BRN-4 barrels use the same piston rod assembly, so your choice of gas block and barrel length determines the system's function—a simpler, more modular approach than caliber-dependent gas tubes. Installation requires torquing the barrel nut to 50–80 foot-pounds. This is a precision component for builders who want genuine HK 416 platform compatibility and the peace of mind that comes from known engineering and fit.

Key Features

• 10.4-inch barrel length optimized for compact, close-quarters rifle builds
• Heavy profile design maximizes rigidity and minimizes flex
• Deep black phosphate finish—hard, durable, and easy to clean inside and out
• 5.56x45 NATO chamber compatible with .223 Remington ammunition
• 1:7 twist rate suitable for standard and heavier 5.56 projectiles
• ½-28 muzzle threads for universal suppressor and muzzle-device fitment
• Extended barrel extension for robust upper receiver interface
• HK 416 compatible; integrates with BRN-4 bolt carrier group and gas block system

Specifications

Frequently Asked Questions

Will this barrel fit my HK 416 or AR platform?

This barrel is machined specifically for early HK 416 upper receivers and the Brownells BRN-4 platform. It features an extended barrel extension designed to integrate with those systems. If you're building a standard AR-15 or modern HK 416, confirm your upper receiver is BRN-4 compatible before purchasing.

What gas block and bolt carrier group do I need?

The BRN-4 barrel works with the BRN-4 bolt carrier group and requires a BRN-4-specific gas block. All BRN-4 barrels share the same piston rod assembly, so you'll select your gas block based on the barrel length—check Brownells' gas block part numbers 078-000-708 and 078-000-709 to match your setup. You'll also need the gas block coil pins (430-103-127) for final assembly.

Can I shoot .223 Remington out of this 5.56 NATO barrel?

Yes. The 5.56x45 NATO chamber readily accepts .223 Remington ammunition, so you have the flexibility to run either cartridge type.

What muzzle devices will fit the ½-28 threads?

The ½-28 muzzle thread pitch is standard in the modern rifle marketplace. Suppressors, flash hiders, brakes, and other devices with ½-28 female threads will install directly. Verify your muzzle device specs before purchase to ensure compatibility.