Brownells Brn-15 5.56Mm 11.5'' Bbl .750'' Gas Block Upper Receiver

The Brownells BRN-15 5.56mm 11.5" upper receiver is a complete, US-manufactured upper assembly designed for shooters building a short-barreled rifle (SBR) or pistol platform. This is the upper half you need to pair with your choice of lower receiver, bolt carrier group, and charging handle—a straightforward path to a compact 5.56 NATO setup without the complexity of sourcing individual components. Built around a stress-relieved 4150 CMV barrel and forged 7075-T6 upper receiver, it combines proven materials with practical design touches that make it a solid foundation for defensive, home-defense, or specialized hunting builds.

The 11.5" barrel length sits in that sweet spot for maneuverability and velocity in a short package. The nitride-finished barrel handles the demands of rapid fire without excessive wear, while the 1:7 twist rate stabilizes a wide range of 5.56 loads. Factory installed at 1/2-28 threads, the A2 flash hider is ready to go—or swap for your preferred muzzle device if you have other plans. The .750" gas block works with the factory dimple to keep the system reliable without custom fitting.

The M-LOK handguard extends well past the gas block to give you genuine room for light mounting, grips, or sling attachments. Anti-rotation tabs prevent the handguard from canting relative to the upper receiver, and dual-screw clamping through the barrel nut keeps everything locked in place. Venting toward the rear helps both barrel and handguard shed heat during sustained fire. The forged upper receiver includes M4 feed ramps, an ejection port cover, and a knurled forward-assist pin for straightforward maintenance or replacement. Every piece is American-made and marked to spec.

Keep in mind this is an upper receiver only—you'll need a lower receiver, bolt carrier group, and charging handle to complete the rifle. NFA rules apply if you intend to assemble this into a short-barreled rifle configuration.

Key Features

• 11.5" 4150 CMV barrel with nitride finish and stress relief
• 1:7 twist rate for reliable bullet stabilization across common 5.56 loads
• Forged 7075-T6 upper receiver with M4 feed ramps and ejection port cover
• M-LOK handguard with anti-rotation tabs and dual-screw clamp for zero cant
• Integrated .750" gas block with factory dimple
• A2 flash hider pre-installed at 1/2-28 threads
• Rear handguard venting for faster cooling
• 100% American-made components
• Knurled forward-assist pin for easy future replacement

Specifications

Frequently Asked Questions

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

This is an upper receiver assembly only. You'll need to source a lower receiver, bolt carrier group, and charging handle to complete your build. The upper receiver bolts to any standard AR-15 lower receiver.

Can I use this for a short-barreled rifle (SBR) build?

Yes, the 11.5" barrel is well-suited for SBR platforms. Be aware that NFA rules apply if you intend to assemble this into a short-barreled rifle—you may need to comply with registration and tax stamp requirements depending on your jurisdiction and how the lower receiver is configured.

Is the muzzle device removable?

Yes, the A2 flash hider is installed at factory and can be removed or swapped. On the 16" lightweight model, a lock nut secures the muzzle device—hold it with a wrench and turn the flash hider counterclockwise to remove it.

What is the M-LOK handguard and why is it useful?

M-LOK is a lightweight mounting standard that runs slots along the handguard for attaching lights, lasers, grips, and sling mounts without tools. The handguard on this upper extends well past the gas block, giving you plenty of real estate for accessories while keeping the overall footprint compact for an 11.5" barrel.