Davidson Defense Spartacus 16.5-inch Mid-Gas 1:7 5.56 NATO AR-15 M-Lok Rifle Complete Upper Build

Spartacus 556 Complete Upper Build

The Spartacus 556 is a complete AR-15 upper receiver assembly featuring a 16.5-inch nitride-finished barrel with a 1:7 twist rate, designed for reliable 5.56 NATO performance. This upper includes a freefloat M-Lok handguard, mid-length gas system, USA-made bolt carrier group, and charging handle. The upper receiver uses 7075-T6 aluminum construction with M4 feed ramps, and the barrel features a medium profile for balance between weight and rigidity. The mid-length gas tube and low-profile gas block are tuned for smooth cycling without excessive recoil.

Key Features

• 16.5-inch medium profile nitride barrel with 1:7 twist rate
• Freefloat 15-inch M-Lok handguard with monolithic top rail
• Mid-length gas system with low-profile gas block
• Complete USA-made bolt carrier group included
• M4 mil-spec charging handle and forward assist
• 7075-T6 aluminum upper receiver with M4 feed ramps
• AR-15 A2 flash hider with 1/2x28 thread pitch

Perfect For

• Shooters building AR-15 platforms from a lower receiver
• Mid-range distance shooting and general purpose use
• Builders seeking a complete upper without sourcing individual components
• Users wanting a freefloat setup for improved accuracy potential

Versatile Mid-Length Gas Platform

The mid-length gas system on this upper provides a balance between reliability and recoil management. The gas tube length and low-profile gas block work together to cycle the bolt carrier group smoothly across standard 5.56 NATO ammunition. The 1:7 twist rate stabilizes a wide range of bullet weights, from lighter varmint loads to heavier match-grade rounds.

Monolithic Rail and M-Lok Integration

The freefloat handguard design isolates the barrel from the upper receiver, which can improve shot-to-shot consistency. The integrated monolithic top rail provides a consistent mounting surface, while the M-Lok slots along the sides and bottom allow flexible accessory mounting without rail segments.

USA-Made Bolt Carrier Group

The included bolt carrier group is manufactured in the USA and is compatible with 5.56 NATO, .223 Remington, .300 Blackout, and .350 Legend ammunition. This compatibility allows flexibility if you plan to use this upper on different lower receivers or caliber conversions in the future.

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