Brownells Brn-4 Assembled Upper 16'' Medium Chrome Lined Barrel Black

The Brownells BRN-4 Assembled Upper is a complete, ready-to-run upper receiver assembly built for shooters who want quality AR-15 components without the guesswork. This 16-inch medium profile upper arrives fully assembled with barrel and gas system installed—just add your HK 416-compatible handguard and a 1/2-28 muzzle device, then you're running. It's purpose-built for hunters, competition shooters, and serious recreational marksmen who value durability and reliability over cutting corners.

The heart of the BRN-4 is a chrome-lined, 4150 chrome moly barrel button-rifled by Faxon with a 1-7 twist rate capable of stabilizing heavier projectiles. Chrome-lined barrels have been the standard for hard-use rifles for decades because they resist fouling, extend barrel life, and handle sustained fire without degradation. The matte black phosphate finish provides corrosion resistance and a clean, professional appearance. The barrel nut uses an extended thread design that engages the barrel extension over significantly more surface area than a standard AR-15, delivering a rock-solid, rigid mount—critical for accuracy and reliability.

Inside, you'll find a purpose-built bolt carrier group machined from forged 8620 steel with a chrome bolt precision-machined from 9310 tool steel. The bolt is headspaced before and after barrel installation to guarantee consistent chamber dimensions. The upper receiver itself is machined from billet aluminum to replicate forged upper profiles, finished in hard coat anodizing. A vented gas block reduces rearward gas bleed into the system, and a Magpul ejection port cover plus mil-spec charging handle come standard. Every BRN-4 is test-fired before shipping, so minor brass marks or light fouling in the chamber are normal signs of a quality check.

Assembly is straightforward: handguard slides onto the barrel with a single retention bolt, and any AR-15-pattern 1/2-28 muzzle device threads on without special tools. Brownells recommends an H1 or H2 buffer tube with a carbine spring for optimal cycling, and use of 5.56×45mm NATO ammunition.

Key Features

• Faxon chrome-lined 4150 chrome moly barrel, 1-7 twist rate for heavy projectiles
• Extended barrel nut threads for rigid, precision mounting
• Forged 8620 steel bolt carrier, 9310 tool steel bolt, both precision-machined and headspaced
• Billet aluminum upper receiver with hard coat anodizing
• Vented gas block matched to 16-inch barrel length
• HK 416-pattern handguard compatibility
• 1/2-28 muzzle threads for universal accessory mounting
• Includes Magpul ejection port cover and mil-spec charging handle
• Test-fired before shipment

Specifications

Frequently Asked Questions

What handguard and muzzle devices are compatible with the BRN-4 16-inch upper?

The upper accepts any HK 416-compatible handguard, which slides onto the barrel and secures with a single bolt for tool-free installation. Any AR-15-pattern muzzle device with 1/2-28 threads will fit; no special tools or adapters are needed.

Can I use this upper on any AR-15 lower receiver?

Yes, the BRN-4 is designed to fit standard AR-15 lower receivers.

Does this upper come fully assembled and ready to shoot?

The upper arrives with the barrel and gas system installed and test-fired. You'll need to add a handguard, a 1/2-28 muzzle device, and a lower receiver to complete the rifle. Brownells recommends pairing it with an H1 or H2 buffer tube and carbine spring for optimal operation.

What ammunition is recommended for the BRN-4?

Brownells recommends using newly manufactured, quality 5.56×45mm NATO ammunition for optimal operation.