The Brownells BRN-4 assembled upper receiver with a 10.4-inch chrome-lined barrel is a complete, ready-to-run upper for AR-15 builders and shooters who want proven reliability without the assembly hassle. This isn't a bare receiver—it comes fully assembled with barrel, bolt carrier group, gas system, and charging handle installed, so you can focus on choosing a handguard and muzzle device rather than wrestling with headspacing and staking. Built on Brownells' commitment to durability over shortcuts, the BRN-4 uses quality materials and meticulous assembly practices that show in every detail.
The heart of this upper is a Faxon medium-profile barrel button-rifled from 4150 chrome-moly steel with a 1-7 twist rate, made to handle hard use and heavier projectiles. The chrome-lined bore and chamber—a time-tested choice for duty and hunting rifles—are cleanly applied by Faxon and finished with matte black phosphate for corrosion resistance. Threading is 1/2-28, so you can attach any standard AR-15 muzzle device without special adapters. The bolt carrier group features a one-piece forged 8620 steel carrier, phosphate-finished, paired with a precision-machined 9310 tool steel bolt that's headspaced before and after barrel installation to guarantee safe, consistent performance.
The billet upper receiver is machined to match forged profiles and hard-coat anodized for a clean, durable finish. Assembly quality matters here: the barrel nut uses extended threads for rigid engagement with the barrel extension, is torqued to spec with AeroShell grease, and checked three times to ensure precision. A vented gas block is tuned for the 10.4-inch barrel length and sized to reduce rearward gas, while a piston bushing protects the upper and is secured with threadlocker. Every upper is test-fired before shipment, so minor marks or fouling are normal signs of a tested product. Handguard installation is straightforward—slide it over the barrel and tighten one bolt—and the included Magpul ejection port cover and mil-spec charging handle complete the package. Pair it with an H1 or H2 buffer, carbine spring, and quality 5.56 NATO ammo for optimal cycling.
| Barrel Length | 10.4 inches |
| Barrel Profile | Medium |
| Barrel Material | 4150 Chrome-Moly Steel |
| Barrel Finish | Chrome-Lined, Matte Black Phosphate |
| Twist Rate | 1-7 |
| Muzzle Threads | 1/2-28 |
| Carrier Material | One-Piece Forged 8620 Steel (Phosphate) |
| Bolt Material | 9310 Tool Steel (Chrome) |
| Upper Receiver Material | Billet Aluminum (Hard-Coat Anodized) |
| Handguard Compatibility | HK 416 Compatible |
| Lower Receiver Compatibility | Standard AR-15 |
| Finish | Matte Black |
| Included Accessories | Magpul Ejection Port Cover, Mil-Spec Charging Handle |
The BRN-4 is compatible with HK 416-style handguards. Installation is simple—slide the handguard over the barrel and tighten one bolt. Always follow the handguard manufacturer's specific installation instructions.
Yes. The barrel is threaded 1/2-28, which is the standard AR-15 muzzle thread. Any 1/2-28 muzzle device will fit, and the upper receiver is compatible with common mounting rods and jigs for installation tools.
The upper comes fully assembled with barrel, bolt carrier group, gas system, charging handle, and Magpul ejection port cover. You'll need a handguard, a 1/2-28 muzzle device, a standard AR-15 lower receiver, an H1 or H2 recoil buffer, and a carbine recoil spring to complete the rifle.
Yes. Every BRN-4 upper is test-fired before final packaging. Minor signs of firing, such as brass marks on the shell deflector or light fouling inside, are normal and expected.
Brownells
Brownells
