Brownells Brn-15 5.56Mm 16'' Bbl .625'' Gas Block Upper Receiver

The Brownells BRN-15 5.56mm 16" upper receiver is a ready-to-assemble upper for builders looking to put together a reliable AR-pattern rifle without starting from scratch. This forged Mil-Spec upper comes complete with a nitride-finished 4150 CMV barrel, M4 feed ramps, ejection port cover, and forward assist—everything you need except the bolt carrier group and charging handle. It's American-made from the ground up, built on proven 7075-T6 aluminum that's hardcoat anodized to resist corrosion and wear.

The 16-inch barrel is chambered in 5.56x45mm NATO with a 1-7 twist rate and features a dimpled gas block shoulder for secure, repeatable seating. A2 flash hider comes pinned and ready (note: the lightweight version uses a lock nut for easier removal). The handguard is where Brownells added smart details—an M-LOK platform extends generously forward, with anti-rotation tabs that lock it to the upper receiver to eliminate any shift or cant relative to the Picatinny rail. Dual clamping screws pass through a properly torqued barrel nut, and vented design lets heat escape during shooting or training. Whether you're building your first AR or your fifth, this upper gives you a solid foundation without compromise.

All barrels are stress-relieved and marked with caliber and twist specs. The 1/2-28 muzzle threads accept standard AR suppressors and muzzle devices. Simply pair this upper with your choice of lower receiver, bolt carrier group, and charging handle to complete the build.

Key Features

• 16-inch 4150 CMV barrel, 1-7 twist, nitride finished
• 5.56x45mm NATO chamber with M4 feed ramps
• Forged Mil-Spec 7075-T6 upper receiver, hardcoat anodized
• M-LOK handguard with anti-rotation tabs and dual clamp screws
• Ejection port cover and knurled forward assist pin
• A2 flash hider installed (lock nut on lightweight version)
• Dimpled gas block shoulder for .625" gas block
• 1/2-28 muzzle threads
• 100% American made

Specifications

Frequently Asked Questions

What do I need to complete this upper receiver?

This upper comes assembled and ready to attach to a lower receiver, but you'll need to source a bolt carrier group and charging handle separately. Once you have those three components (upper, lower, BCG, and charging handle), your AR will be complete and functional.

Can I use a suppressor on this barrel?

Yes. The barrel is threaded 1/2-28 and comes with an A2 flash hider installed. You can unscrew the flash hider (note: the lightweight version uses a lock nut that must be secured with a wrench before removal) and install any standard 1/2-28 suppressor or muzzle device.

What gas block size does this upper use?

The barrel features a .625-inch gas block dimple. This is the standard rifle-length gas block diameter and accepts common .625" gas blocks for your build.

Is this upper receiver compatible with standard AR-15 lowers?

Yes, this is a Mil-Spec forged upper receiver with M4 feed ramps, designed to work with standard AR-15 lower receivers. It will mate with any mil-spec or commercial lower.