The Brownells BRN-4 Assembled Upper with 10.4" Heavy Chrome Lined Barrel is a complete, ready-to-configure upper receiver built for shooters who want professional quality without assembly hassle. This is a true plug-and-play upper—barrel, gas system, and bolt carrier are already installed and headspaced. All you need to add is an HK 416-compatible handguard and a 1/2-28 muzzle device to have a functional rifle. It's the smart choice for builders who value accuracy and durability over starting from scratch.
The barrel itself is where this upper earns its reputation. Brownells specs Faxon's medium-profile barrel, button-rifled from 4150 chrome moly steel with a chrome-lined bore and chamber—the same hard-use standard trusted by professional shooters and military users for decades. The 1-7 twist rate handles heavy projectiles, and the matte black phosphate finish resists corrosion. The barrel extension threads engage the barrel nut over a significantly larger surface than standard AR-15 uppers, ensuring rigid mounting. Brownells torques the barrel nut three times with AeroShell Grease 64 to guarantee proper spec.
The bolt carrier group is built from the ground up: a one-piece forged 8620 steel carrier with a phosphate finish, paired with a precision 9310 tool steel bolt that's headspaced before and after barrel installation. The billet upper receiver is machined from solid aluminum and finished with matte black hard coat anodizing—you'll see the machine marks, a sign of quality billet work. The gas block is vented forward to reduce rearward gas impulse, and the piston bushing is secured with blue threadlocker to prevent accelerated wear. Includes a Magpul ejection port cover and mil-spec charging handle. Every upper is test-fired before shipping. Brownells recommends an H1 or H2 recoil buffer with a carbine recoil spring for optimal function and use of 5.56x45mm NATO quality ammunition.
Note: NFA rules apply. Handguard and muzzle device sold separately.
| Brand | Brownells |
| Model | BRN-4 Assembled Upper |
| Barrel Length | 10.4" |
| Barrel Profile | Medium, Heavy |
| Barrel Material | 4150 Chrome Moly Steel |
| Bore | Chrome Lined |
| Twist Rate | 1-7 |
| Muzzle Threads | 1/2-28 |
| Bolt Carrier Material | Forged 8620 Steel (one-piece) |
| Bolt Material | 9310 Tool Steel |
| Upper Receiver Material | Billet Aluminum |
| Upper Receiver Finish | Matte Black Hard Coat Anodize |
| Barrel Finish | Matte Black Phosphate |
| Handguard Compatibility | HK 416 Compatible |
| Lower Receiver Compatibility | Standard AR-15 |
| Included Accessories | Magpul Ejection Port Cover, Mil-Spec Charging Handle |
Yes. The BRN-4 Assembled Upper is designed to fit standard AR-15 lower receivers. Simply attach it to your lower, install an HK 416-compatible handguard, add a 1/2-28 muzzle device, and you're ready to shoot.
The upper uses an HK 416-compatible handguard interface. Handguards slide over the barrel and secure with one bolt. For muzzle devices, any standard AR-15 device with 1/2-28 threads will fit. Both handguard and muzzle device are sold separately and are not included.
The barrel, gas system, and bolt carrier group are all installed and headspaced. However, you still need to add an HK 416-compatible handguard and a 1/2-28 muzzle device before the rifle is functional. It's ready to configure, not ready to shoot out of the box.
Brownells recommends 5.56x45mm NATO newly manufactured quality ammunition for optimal operation.
Brownells recommends an H1 or H2 recoil buffer paired with a carbine recoil spring for optimal function.
Brownells
Brownells
Brownells
