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

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

This is a complete AR-15 upper 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. A complete M16 profile bolt carrier group and a Mil-Spec M4 charging handle complete the upper component set.

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
• Complete M16 profile bolt carrier group, .223 Rem, 5.56 NATO, .300 BLK, .350 Legend compatible
• Mil-Spec AR-15 M4 charging handle
• GI Birdcage flash hider, steel, 5-8x24 thread pitch
• Black 5-8-inch crush washer

Perfect For

• AR-15 pistol builders pairing a complete .300 BLK upper with an existing lower
• Shooters adding a 10.5-inch pistol-length .300 BLK upper to an AR-15 lower they already own
• Builders who want a BCG and charging handle included with a classic FSB and quad rail pistol upper assembly

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.

Bolt Carrier Group and Charging Handle

The complete M16 profile bolt carrier group is compatible with .223 Remington, 5.56 NATO, .300 Blackout, and .350 Legend, making it a versatile and well-suited choice for this chambering. The Mil-Spec M4 charging handle pairs with the BCG inside the upper receiver to complete the upper interior. These two components complete the upper component set alongside the upper assembly, barrel, and handguard.

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 upper.

Follow safe handling and manufacturer instructions. Ensure compliance with all applicable federal, state, and local laws.