Davidson Defense Breacher Up 10.5-inch Pistol-Gas 1:8 .300 BLK AR-15 FSB Quad-Rail Pistol Upper Build Kit

Breacher Up 10.5-Inch Pistol-Gas 1-8 .300 BLK AR-15 FSB Quad-Rail Pistol Upper Build Kit

This is an AR-15 upper build kit chambered in .300 AAC Blackout, built around a 10.5-inch government profile 4150 CrMoV steel barrel with a 1-8 twist rate and a pistol-length gas system. The upper assembly is built on a 7075-T6 aluminum upper receiver with an anodized finish, M4 feed ramps, a standard forward assist, and a .223 and 5.56 dust cover assembly. The barrel carries a USA-made steel A2 front sight with a complete sight post, plunger, and spring, and a separate adjustable skeletonized clamp-on gas block at .750 inch positioned under the handguard that drives the pistol-length gas system independently of the front sight. The 7-inch M4 carbine drop-in quad rail with a Colt-style delta ring assembly covers the forend. BCG and charging handle are not included.

Key Features

• .300 AAC Blackout chambering, 10.5-inch government profile 4150 CrMoV steel barrel, black finish
• 1-8 twist rate, 5-8x24 thread pitch
• Pistol-length gas system with pistol-length gas tube
• Adjustable skeletonized clamp-on gas block, .750 inch, under handguard
• USA-made steel A2 front sight with sight post, plunger, and spring
• 7075-T6 aluminum upper receiver, anodized, M4 feed ramps
• Standard AR-15 forward assist assembly
• .223 and 5.56 dust cover assembly
• 7-inch M4 carbine drop-in quad rail, black, Colt-style delta ring assembly
• GI Birdcage flash hider, steel, 5-8x24 thread pitch
• Black 5-8-inch crush washer

Perfect For

• AR-15 pistol builders sourcing a .300 BLK upper assembly without BCG or charging handle
• Shooters adding a 10.5-inch pistol-length .300 BLK upper to an existing lower with a BCG and charging handle on hand
• Builders who want a classic FSB and quad rail front end in a compact pistol-length .300 BLK upper kit

Upper Assembly and Gas System

The 7075-T6 aluminum upper receiver with an anodized finish and M4 feed ramps forms the core of the front end, with a standard forward assist assembly and a .223 and 5.56 dust cover assembly built in. The 10.5-inch government profile 4150 CrMoV steel barrel carries a USA-made steel A2 front sight with a complete sight post, plunger, and spring at the carbine-length position on the barrel. The A2 front sight on this build is a sight-only component and does not serve as the gas block. The actual gas system is driven by a separate adjustable skeletonized clamp-on gas block at .750 inch that sits under the handguard at the pistol-length gas port position on the barrel, with a pistol-length gas tube running from the gas block back to the upper receiver. This configuration delivers a true pistol-length gas system while retaining the classic A2 front sight post aesthetic above the handguard line. The 7-inch M4 carbine drop-in quad rail with a Colt-style delta ring assembly covers the barrel and gas block along the forend, providing full Picatinny rail coverage on all four sides for accessory attachment.

Muzzle Device

The GI Birdcage flash hider in steel threads onto the 5-8x24 muzzle end of the barrel and closes out the front of this pistol-length upper with a standard proven flash hider pattern compatible with .300 Blackout at the 5-8x24 thread pitch. The included black 5-8-inch crush washer seats at the barrel shoulder and completes the muzzle hardware for this kit.

Follow safe handling and manufacturer instructions. Ensure compliance with all applicable federal, state, and local laws. BCG and charging handle are not included.