The Brownells BRN-4 assembled upper receiver with 13.7" medium chrome-lined barrel gives you a complete, ready-to-run upper that bridges the gap between bare components and a finished rifle. Built to HK 416-pattern specs on a billet upper, this 5.56 NATO upper is designed for shooters who want a quality assembled upper without the guesswork—just add your choice of HK 416-compatible handguard, thread on a 1/2-28 muzzle device, and mount it to any standard AR-15 lower to get to the range.

The 13.7" barrel is medium profile 4150 chrome-moly steel, button-rifled by Faxon with a 1-7 twist rate that handles everything from standard 5.56 to heavier projectiles. The chrome-lined bore and chamber—a time-tested choice for duty and hard-use rifles—is finished with matte black phosphate for corrosion resistance. The barrel nut engages with extended threads for a rigid fit, torqued and re-torqued to spec and backed with proper lubrication. All work is done at the factory; the upper ships test-fired and ready.

Inside, you'll find a fresh bolt carrier group: one-piece forged 8620 steel carrier with phosphate finish, paired with a 9310 tool steel bolt that's precision-machined and headspaced before and after barrel installation. The billet upper receiver is machined to mirror forged contours and finished in matte black hard coat anodizing. A piston bushing is installed and secured to prevent wear on the aluminum. You also get a Magpul ejection port cover and mil-spec charging handle included. Gas block venting is designed to minimize rearward gas bleed into the system.

Handguard and muzzle device installation are straightforward—the 1/2-28 threaded barrel accepts any standard AR-15 muzzle device, and the HK 416 handguard slide-and-bolt system is fast and simple. Brownells recommends an H1 or H2 recoil buffer with carbine spring for optimal function and quality 5.56 NATO ammunition.

Key Features

• 13.7" medium profile Faxon barrel, 4150 chrome-moly steel, 1-7 twist
• Chrome-lined bore and chamber for durability and corrosion resistance
• Billet upper receiver with matte black hard coat anodize
• One-piece forged 8620 steel carrier; 9310 tool steel bolt, headspaced at factory
• Extended barrel nut threads for rigid mounting; torqued to spec with proper lubrication
• HK 416-compatible handguard interface
• 1/2-28 muzzle threads for any standard AR-15 muzzle device
• Magpul ejection port cover and mil-spec charging handle included
• Piston bushing installed to protect upper receiver aluminum
• Factory test-fired and ready to run

Specifications

Frequently Asked Questions

What AR-15 lower will this upper fit?

The BRN-4 upper is built to standard AR-15 specifications and will mate with any standard AR-15 lower receiver.

What handguards are compatible with this upper?

The BRN-4 uses an HK 416-compatible handguard interface. Any handguard designed for HK 416 pattern will work; installation is simple—slide the handguard over the barrel and tighten one bolt.

What muzzle devices can I use?

The barrel features 1/2-28 threads, which is the standard AR-15 muzzle thread pattern. Any 1/2-28 muzzle device—flash hiders, suppressors, brakes—will fit and is compatible with standard AR-15 installation tools and jigs.

What buffer weight should I use?

Brownells recommends an H1 or H2 recoil buffer paired with a carbine recoil spring for optimal operation.