Davidson Defense Darkstar 18-inch Rifle-Gas 1:7.5 6mm ARC AR-15 Freefloat M-Lok Rifle Upper Build Kit

Darkstar 18-Inch Rifle-Gas 1-7.5 6mm ARC AR-15 Freefloat M-LOK Rifle Upper Build Kit

This is an AR-15 upper build kit chambered in 6mm ARC, built around an 18-inch government profile 41V50 CrMoV steel barrel with a nitride finish, 5R rifling, and a 1-7.5 twist rate. The slick side billet upper receiver in USA-made 6061 aluminum with an anti-rotation cutout anchors the front end with a cleaner exterior profile than a standard forged receiver. The 15-inch freefloat extended quad rail M-LOK handguard clamps onto the upper and runs the forend with full quad rail coverage and M-LOK slots across the handguard body. BCG and charging handle are not included.

Key Features

• 6mm ARC chambering, 18-inch government profile 41V50 CrMoV steel barrel, nitride finish
• 1-7.5 twist rate, 5R rifling, 5-8x24 thread pitch, .750 inch gas block journal
• Rifle-length gas system with rifle-length stainless steel gas tube
• Micro low-profile steel gas block, .750 inch
• USA-made 6061 aluminum slick side billet upper receiver, anti-rotation cutout
• 15-inch freefloat extended quad rail M-LOK handguard, clamp-on, black
• GI Birdcage flash hider, 5-8x24 thread pitch, .308, 7.62x39, .300 BLK compatible
• Black 5-8-inch crush washer

Perfect For

• AR-15 builders sourcing a 6mm ARC upper assembly without BCG or charging handle
• Shooters adding an 18-inch 6mm ARC upper to an existing lower with a BCG and charging handle on hand
• Builders who want a slick side billet upper and quad rail handguard in one 6mm ARC upper kit

Upper Receiver and Barrel

The USA-made 6061 aluminum slick side billet upper receiver sets this front end apart from standard forged uppers with a clean exterior that removes the forward assist boss entirely, giving the upper a streamlined profile. The anti-rotation cutout is a precision fit feature specific to this billet receiver design. The 18-inch government profile 41V50 CrMoV steel barrel brings a nitride finish, 5R rifling, and a 1-7.5 twist rate to the 6mm ARC chamber, threaded at 5-8x24 with a .750 inch gas block journal. The rifle-length stainless steel gas tube and micro low-profile steel gas block at .750 inch run a full rifle-length gas system along the barrel, keeping the dwell time and gas timing appropriate for the 18-inch barrel profile.

Freefloat Extended Quad Rail M-LOK Handguard

The 15-inch freefloat extended quad rail M-LOK handguard clamps onto the upper receiver and surrounds the barrel and gas system along the forend with full Picatinny rail coverage on all four sides and M-LOK slots integrated into the handguard body. The clamp-on design attaches directly to the upper receiver without anti-rotation tabs, keeping the installation hardware minimal. The combination of quad rail sections and M-LOK slots gives this build maximum accessory flexibility across all positions on the forend, making it a well-suited front end for a purpose-built 6mm ARC rifle platform.

Muzzle Device

The GI Birdcage flash hider threads onto the 5-8x24 muzzle end of the barrel and finishes the front of the upper with a standard proven flash hider pattern compatible with .308, 7.62x39, and .300 Blackout thread pitch muzzle devices. The included black 5-8-inch crush washer seats at the barrel shoulder and completes the muzzle hardware for this kit.

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