Spartacus 16-Inch Pistol-Gas .300 Blackout AR-15 M-Lok Handguard Rifle Full Build Kit

This complete .300 Blackout AR-15 build kit combines a 16-inch 4150 CrMoV barrel with a freefloat M-Lok handguard, mil-spec components, and everything needed to assemble a functional rifle. The pistol-length gas system pairs with a 1:8 twist rate optimized for .300 Blackout ammunition, making this configuration ideal for subsonic loads and suppressed shooting.

Key Features

• 16-inch 4150 CrMoV barrel, 1:8 twist rate, phosphate finish
• Freefloat 15-inch M-Lok handguard with monolithic top rail
• Pistol-length gas system with low-profile gas block
• Complete mil-spec lower parts kit, buffer tube, buffer, and recoil spring
• AR-15 bolt carrier group compatible with .300 Blackout, 5.56 NATO, and .223 Remington
• M4 mil-spec charging handle and forward assist assembly
• GI birdcage flash hider with 5/8x24 thread pitch
• Special Operations AR-15 stock included

Perfect For

• Builders seeking a complete .300 Blackout platform without the serialized lower receiver
• Shooters planning suppressed or subsonic configurations
• Those wanting a compact, maneuverable rifle with pistol-length gas cycling
• Intermediate builders comfortable with lower receiver completion

Optimized for Subsonic Performance

The 1:8 twist rate and pistol-length gas system work together to stabilize heavier .300 Blackout loads, particularly subsonic ammunition commonly paired with suppressors. This configuration reduces felt recoil compared to full-power loads while maintaining reliability across standard and subsonic rounds. The freefloat handguard isolates the barrel from external pressure, supporting consistent accuracy across varying ammunition types.

Mil-Spec Foundation with Modern Ergonomics

This kit pairs traditional mil-spec lower components with a modern upper receiver design. The 7075-T6 aluminum upper receiver features M4 feed ramps and black anodized finish. The monolithic top rail on the M-Lok handguard provides integrated mounting for optics and accessories without requiring separate rail segments.

Complete Component Breakdown

The kit includes the upper assembly, bolt carrier group, charging handle, lower parts kit, buffer tube, buffer, recoil spring, castle nut, end plate, and stock. Lower receiver not included. The GI birdcage flash hider threads at 5/8x24, standard for .300 Blackout platforms and compatible with most aftermarket suppressors designed for this caliber.

Gas System and Cycling

Pistol-length gas tubes cycle faster than carbine-length systems, reducing dwell time and supporting reliable function with both standard and subsonic .300 Blackout ammunition. The micro low-profile gas block (.750" diameter) minimizes weight while maintaining durability under sustained fire.

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