Brownells Brn-Gau-5A Upper Receiver, 12.7'' 1-12 Twist, Pin/Weld, Black

The Brownells BRN-GAU-5A upper receiver in 12.7" with 1-12 twist is built for shooters who want an authentic retro rifle build with modern compliance. This upper takes its design cues from early carbine configurations and the classic XM177/GAU-5 platform, bringing that vintage aesthetic to a modern 16"-plus overall length firearm. The 12.7" barrel has its muzzle device pinned and welded, meeting legal rifle length requirements while preserving the character of original carbine moderators. If you're assembling a retro-correct AR or just appreciate the clean lines of M16-era rifle design, this upper delivers both historical accuracy and practical function.

The upper features an M16 slick-side receiver—no forward assist, no shell deflector—paired with proper M16A1 ejection port cover with that distinctive external bump. The flash hider sports the iconic XM177 grenade-ring profile, managing muzzle signature with a design inspired by the originals. You get carbine-length black polymer handguards with integrated heatshields that echo the CAR-style furniture of the era, plus a properly tapered slip ring at the barrel shoulder, all details that matter to builders chasing period-correct aesthetics.

Under the hood: chrome-lined bore and chamber, mil-spec manganese phosphate finishing, and a complete manganese phosphate bolt carrier group with 9310 bolt ready to function. The A1 rear sight aperture adjusts easily with a cartridge or field tool. The 1-12 twist barrel stabilizes rounds across the 5.56x45mm NATO range, giving you flexibility whether you're running lighter or heavier ammunition. This is a complete upper assembly—you're getting the barrel, bolt carrier, front sight base, and handguards all together, simplifying your build.

Whether you're documenting Vietnam-era rifle history or simply prefer the ergonomics and look of early carbine guns, this Brownells upper respects the original while meeting today's legal and practical requirements.

Key Features

• M16 slick-side receiver with proper M16A1 ejection port cover
• 12.7" barrel with 1-12 twist rate in 5.56x45mm NATO
• Muzzle device pinned and welded for 16"-plus overall length compliance
• XM177 grenade-ring flash hider for period-correct appearance
• Chrome-lined bore and chamber for durability
• Carbine polymer handguards with heatshields and tapered slip ring
• Complete mil-spec manganese phosphate bolt carrier group with 9310 bolt
• A1 aperture rear sight assembly
• Front sight base (not F-marked) for proper sight alignment with carry handle

Specifications

Frequently Asked Questions

Will this upper work with a standard AR-15 lower receiver?

Yes, this is a standard mil-spec upper receiver that will mate with any mil-spec AR-15 lower receiver.

Is the muzzle device permanently attached?

Yes, the XM177 flash hider on this 12.7" upper is pinned and welded in place to achieve the required 16"-plus overall rifle length.

What's included with this upper?

This is a complete upper assembly that comes with the barrel, bolt carrier group, handguards, front sight base, rear sight, and flash hider already installed.

Is this upper suitable for retro AR builds?

Absolutely. The M16 slick-side receiver, period-correct ejection port cover, XM177 flash hider profile, carbine handguards, and tapered slip ring are all designed to match the aesthetic and function of early carbine configurations.