Brownells Brn-15 5.56Mm 13.7'' Bbl .750'' Gas Block Upper Receiver

The Brownells BRN-15 5.56mm upper receiver with 13.7" barrel and .750" gas block is a US-manufactured upper assembly built for shooters who want a complete, ready-to-pair platform without assembling from loose parts. This forged upper comes with a nitride-finished 4150 CMV barrel, M4 feed ramps, ejection port cover, and forward assist—everything you need except a bolt carrier group and charging handle. It's ideal for AR builders and gunsmiths looking to start with a proven, American-made foundation.

The 13.7" barrel is threaded 1/2-28 and ships with an A2 flash hider, tuned for 5.56 NATO with a 1:7 twist rate suited to a wide range of bullet weights. The .750" gas block mounting surface (dimpled for secure screw engagement) keeps the gas system reliable and repeatable. Stress-relieved barrel construction helps maintain accuracy over time and thermal cycles.

The handguard is where Brownells made smart design choices: it's M-LOK compatible, extends past the gas block to maximize mounting real estate, and features anti-rotation tabs that lock it to the upper receiver's Picatinny rail—no cant, no surprises. Large dual screws clamp through a properly torqued barrel nut, preventing creep. Strategic cooling vents near the rear let both barrel and handguard shed heat quickly during extended shooting sessions.

The forged 7075-T6 upper receiver is hardcoat anodized to Mil-Spec standards, with a knurled forward assist pin for easy future swaps. This is a no-compromise, no-frills assembly: 100% US-made components, marked and documented, ready to marry to your choice of BCG and charging handle.

Key Features

• Forged 7075-T6 upper receiver, hardcoat anodized, Mil-Spec M4 feed ramps
• 13.7" barrel, 5.56 NATO, 1:7 twist, 4150 CMV steel, nitride finished, stress relieved
• .750" gas block dimple for secure, repeatable gas system mounting
• A2 flash hider, 1/2-28 threaded muzzle
• M-LOK handguard with anti-rotation tabs and dual-screw barrel nut clamp
• Ejection port cover and knurled forward assist pin
• 100% American manufactured

Specifications

Frequently Asked Questions

What do I need to complete this upper receiver?

This upper assembly does not include a bolt carrier group or charging handle. You'll need to source and install both to have a functional rifle. Once paired with those components and a lower receiver, you'll have a complete rifle.

Is this upper compatible with standard AR-15 lower receivers?

Yes. This is a forged Mil-Spec upper receiver that mates to standard AR-15 lower receivers with conventional takedown pins and trigger groups.

What kind of handguard and rail system does it have?

The upper features a M-LOK compatible handguard with anti-rotation tabs that lock into the receiver's Picatinny rail, eliminating cant. The handguard extends past the gas block and includes venting for cooling.

Can I swap out the A2 flash hider?

Yes. The muzzle is threaded 1/2-28. Note: the 16" lightweight model includes a lock nut on the flash hider; to remove it, secure the lock nut with a wrench, turn toward the rear, and unscrew the flash hider.