Brownells Brn-4 5.56Mm 16'' Med Bbl Complete Upper W/13.5'' Handguard

The Brownells BRN-4 5.56mm complete upper receiver is a ready-to-run assembly that lets you build or upgrade an AR-15 without waiting for parts to trickle in. This 16-inch medium-barrel upper arrives fully assembled with a 13.5-inch Midwest Industries handguard, muzzle device, and gas system—all you need is a lower receiver to get shooting. It's the kind of no-fuss solution that appeals to builders who want quality without the assembly headache, and to shooters who just want to get to the range.

Built entirely from new components, the BRN-4 starts with a Faxon barrel in 5.56x45mm NATO with a 1-7 twist and medium profile that strikes a balance between weight and rigidity. The bolt carrier group uses a forged 8620 steel carrier with a precision 9310 tool steel bolt, both headspaced to tight tolerances before and after barrel installation. The upper receiver itself is machined from billet aluminum and finished in matte black hard coat anodizing—a more rigid platform than typical forged uppers, with lengthier barrel nut threads that lock the barrel extension over a larger surface area. Brownells test-fires every upper before it ships, so you may see minor brass marks or fouling as evidence of that QC step.

The 13.5-inch Midwest Industries handguard gives you plenty of mounting real estate with full M-LOK attachment points along its length and a continuous picatinny rail for optics and accessories. The included Magpul ejection port cover and mil-spec charging handle round out the package. For reliable operation, Brownells recommends pairing this upper with an H1 or H2 recoil buffer and carbine recoil spring on your lower, and feeding it quality 5.56x45mm NATO ammunition.

Key Features

• 16-inch medium-profile Faxon barrel, 5.56x45mm NATO, 1-7 twist, 1/2-28 muzzle
• Billet-machined upper receiver with matte black hard coat anodizing for durability and precision fit
• 13.5-inch Midwest Industries handguard with full M-LOK and picatinny rail coverage
• Forged 8620 steel carrier with 9310 tool steel bolt, both headspaced and test-fired
• Extended barrel nut threads for rigid barrel mounting and repeated torque verification
• Gas block matched to 16-inch barrel length with forward venting to reduce carrier tilt
• Includes Magpul ejection port cover and mil-spec charging handle
• Test-fired and inspected before shipment

Specifications

Frequently Asked Questions

What do I need to complete this upper into a working rifle?

This is a complete upper assembly, so you'll need an AR-15 lower receiver to mate it with. Brownells also recommends using an H1 or H2 recoil buffer paired with a carbine recoil spring for optimal operation.

What barrel profile does this come with?

The 16-inch barrel uses a medium profile, which balances weight and heat dissipation while maintaining enough material to resist barrel shift during extended shooting.

What kind of handguard is included?

A 13.5-inch Midwest Industries handguard with both full-length picatinny rail and M-LOK attachment points, giving you flexibility to mount optics, lights, and other accessories.

Is the barrel and bolt headspaced before I receive it?

Yes. The bolt is headspaced prior to barrel installation, then again after, to ensure proper fit. The entire upper is test-fired and inspected before shipment.