The Brownells BRN-4 5.56mm complete upper receiver with 16-inch heavy barrel and 13.5-inch handguard is a purpose-built assembly that lets you finish an AR-15 build without the guesswork. This isn't a stripped upper—it comes fully assembled with barrel, bolt carrier group, gas system, charging handle, and Magpul ejection port cover ready to marry to your lower receiver. For hunters, precision shooters, and sport rifle builders who want a known-quality foundation without hand-selecting and fitting components separately, this is a solid shortcut.

The heart of the BRN-4 is an all-new bolt carrier group machined from forged 8620 steel with a hard nitride finish, paired with a 9310 tool steel bolt that's been headspaced before and after barrel installation. The 16-inch Faxon barrel is button rifled with a 1:7 twist, chambered in 5.56x45mm NATO, and finished in a heavy profile—that extra mass reduces heat distortion during sustained fire and helps hold tight groups as the barrel climbs in temperature. The billet upper receiver is matte black hard-coat anodized and features extended barrel nut threads that grip the barrel extension over a significantly larger contact area than a standard AR-15, then torqued to spec with the barrel nut reinstalled three times for consistency.

The 13.5-inch Midwest Industries handguard delivers plenty of rail real estate with a full-length Picatinny top and multiple M-LOK slots for optics, lights, and other accessories. Forward-vented gas block design reduces rearward gas volume, keeping the system balanced. Brownells recommends pairing this upper with an H1 or H2 recoil buffer and carbine spring, and using quality 5.56x45mm NATO ammunition. Every assembly is test-fired before shipping—you may notice minor brass marks or residue from that proof.

The Brownells BRN-4 5.56mm complete upper receiver with 16-inch heavy barrel and 13.5-inch handguard is a purpose-built assembly that lets you finish an AR-15 build without the guesswork. This isn't a stripped upper—it comes fully assembled with barrel, bolt carrier group, gas system, charging handle, and Magpul ejection port cover ready to marry to your lower receiver. For hunters, precision shooters, and sport rifle builders who want a known-quality foundation without hand-selecting and fitting components separately, this is a solid shortcut.

The heart of the BRN-4 is an all-new bolt carrier group machined from forged 8620 steel with a hard nitride finish, paired with a 9310 tool steel bolt that's been headspaced before and after barrel installation. The 16-inch Faxon barrel is button rifled with a 1:7 twist, chambered in 5.56x45mm NATO, and finished in a heavy profile—that extra mass reduces heat distortion during sustained fire and helps hold tight groups as the barrel climbs in temperature. The billet upper receiver is matte black hard-coat anodized and features extended barrel nut threads that grip the barrel extension over a significantly larger contact area than a standard AR-15, then torqued to spec with the barrel nut reinstalled three times for consistency.

The 13.5-inch Midwest Industries handguard delivers plenty of rail real estate with a full-length Picatinny top and multiple M-LOK slots for optics, lights, and other accessories. Forward-vented gas block design reduces rearward gas volume, keeping the system balanced. Brownells recommends pairing this upper with an H1 or H2 recoil buffer and carbine spring, and using quality 5.56x45mm NATO ammunition. Every assembly is test-fired before shipping—you may notice minor brass marks or residue from that proof.