Davidson Defense Marathon 14.5" 5.56 NATO AR-15 Pistol Build Kit, KAK A2 Flash Hider, w/ SBA3 Brace

Marathon 14.5" 5.56 NATO AR-15 Pistol Build Kit, KAK A2 Flash Hider, w/ SBA3 Brace

The Marathon 14.5-inch Pistol Build Kit delivers a complete upper and lower receiver setup in 5.56 NATO with carbine-length gas system tuning. This full build kit includes everything except the serialized lower receiver, paired with the SB Tactical SBA3 adjustable brace and a KAK Industry A2 extended flash hider. The 12-inch M-LOK handguard provides modern mounting flexibility while the government profile barrel with 1:7 twist handles standard and heavier ammunition reliably.

Key Features

• 14.5-inch 4150 CrMoV barrel with government profile and 1:7 twist rate for 5.56 NATO
• Carbine-length gas system with 0.750 gas block for balanced cycling
• 12-inch M-LOK aluminum handguard with anodized finish
• SB Tactical SBA3 adjustable brace for customizable length of pull
• Complete bolt carrier group in 9310 nitride-finished steel
• Mil-spec M4 charging handle included
• KAK Industry A2 extended flash hider with pin/weld ready design
• Full lower parts kit with all internal components

Perfect For

• Shooters building a compact home defense or range pistol
• Builders seeking a complete kit with minimal additional purchases
• Those preferring the SBA3 brace for adjustability and comfort
• Pistol platforms optimized for 5.56 NATO ballistics

Pin/Weld Ready Setup

The KAK Industry A2 extended flash hider ships pin/weld ready, meaning the muzzle device can be permanently attached to meet local compliance requirements when needed. This design accommodates builders who want to configure their setup based on their specific legal jurisdiction and intended use. The pin/weld ready feature provides flexibility without forcing a particular configuration.

Carbine-Length Gas System Performance

This build uses carbine-length gas tuning, which cycles reliably with the 14.5-inch barrel and standard ammunition. The 0.750 gas block size matches the carbine system specification, delivering consistent bolt carrier movement and ejection patterns. The government profile barrel pairs well with this gas length for shooters who want proven, predictable performance without exotic tuning requirements.

Complete Upper and Lower Assembly

The kit includes the complete upper receiver assembly with barrel and handguard already installed, plus a full lower parts kit with all springs, pins, and trigger components. The bolt carrier group and charging handle ship ready for assembly. Lower receiver not included.

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