Davidson Defense Marathon 14.5" 5.56 NATO AR-15 Pistol Build Kit, KAK A2 Flash Hider, w/ Magpul BTR Brace

Marathon 14.5" 5.56 NATO AR-15 Pistol Build Kit, KAK A2 Flash Hider, w/ Magpul BTR Brace

This is a complete pistol build kit built around a 14.5-inch carbine-gas barrel in 5.56 NATO. You get everything needed to assemble a functional AR-15 pistol except the serialized lower receiver. The kit pairs a Black Diamond billet upper receiver with a 12-inch M-LOK handguard, a carbine-length gas system, and a Magpul BTR brace for stable handling.

Key Features

• 14.5-inch 5.56 NATO barrel with 1:7 twist rate and carbine-gas system
• KAK Industry A2 extended flash hider, pin/weld ready
• Black Diamond Series billet upper receiver with anodized finish
• 12-inch AR-15 ultra-lightweight M-LOK handguard in aircraft-grade aluminum
• Complete bolt carrier group in 9310 alloy steel with nitride finish
• Magpul BTR pistol brace for ergonomic support and control
• Mil-spec heavy-duty buffer tube with standard carbine recoil spring and 3 oz buffer
• Mil-spec M4 charging handle included

Perfect For

• Shooters building a compact 5.56 NATO platform with pistol configuration
• Buyers seeking a lightweight, modular upper with M-LOK mounting compatibility
• Those wanting a pin/weld ready muzzle device setup for future suppressor mounting
• Builders who prefer billet upper receivers for precision and durability

Carbine-Gas Performance and Reliability

The carbine-length gas system is tuned for 14.5-inch barrels and delivers reliable cycling across standard and quality ammunition. This gas length balances bolt carrier velocity with manageable recoil impulse, making it predictable for rapid follow-up shots. The 1:7 twist rate stabilizes a wide range of bullet weights from 55-grain to 77-grain rounds, giving you flexibility in ammunition selection without accuracy loss.

Upper Assembly and Handguard Design

The Black Diamond billet upper receiver is machined from 6061-T6 aluminum and anodized for corrosion resistance. The 12-inch ultra-lightweight handguard uses aircraft-grade aluminum with M-LOK slots for accessories. This combination keeps overall weight down while maintaining structural rigidity. The handguard length provides good hand positioning without extending past the muzzle device.

Muzzle Device and Pin/Weld Readiness

The KAK Industry A2 extended flash hider threads at 1/2x28 and is pin/weld ready. This means you can permanently attach it to the barrel if you plan to add a suppressor later, keeping your overall length compliant. The flash hider reduces visible muzzle signature in low-light conditions while managing recoil gases effectively.

Magpul BTR Brace and Ergonomics

The Magpul BTR pistol brace offers a comfortable, stable platform for pistol-configured builds. The brace design allows for secure wrist support and improved control during shooting. It's adjustable and compatible with standard buffer tubes, making it a proven choice for pistol builds that prioritize handling and accuracy.

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