Details
Coldfire 8.5-Inch Pistol-Gas 1:8 .300 BLK AR-15 Free-Float M-LOK Handguard Pistol Full Build Kit with SB Tactical SBA3 Brace
The Coldfire Full Build Kit is built around an 8.5-inch .300 Blackout heavy barrel machined from 4150 chrome moly vanadium steel, with a pistol-length gas system and a Parkerized finish. It is paired with a 7-inch black aluminum M-LOK handguard featuring a partial Picatinny top rail section and an SB Tactical SBA3 adjustable pistol stabilizing brace in black polymer, mounted on a mil-spec heavy-duty six-position buffer tube. The kit ships with a complete bolt carrier group rated for 5.56, .223, .300 Blackout, and .350 Legend, along with a mil-spec quality M4 charging handle. The short, heavy barrel keeps the front end compact and sturdy, and the 1:8 twist suits a wide range of bullet weights in .300 Blackout. Lower receiver is not included. Lower parts kit, pistol grip, recoil spring, castle nut, and end plate details were not supplied with this listing.
Key Features
- 8.5-inch heavy profile barrel, 4150 chrome moly vanadium steel, Parkerized finish, 1:8 twist, .300 Blackout, 5/8x24 muzzle threads
- Pistol-length gas system with a micro low-profile gas block sized for a .750-inch barrel
- 7075-T6 aluminum upper receiver with M4 feed ramps, anodized finish
- 7-inch M-LOK handguard, aluminum, black, with partial Picatinny top rail section
- AR-15 TPI GI birdcage flash hider on 5/8x24 threads
- Complete AR-15 bolt carrier group (5.56/.223/.300/.350), 9310 alloy steel carrier, Nitride finish
- Mil-spec quality AR-15 M4 charging handle included
- Mil-spec heavy-duty six-position buffer tube and 3 oz. buffer
- SB Tactical SBA3 adjustable pistol stabilizing brace, polymer, black
- Lower receiver is not included.
Barrel and Gas System
The 8.5-inch barrel is machined from 4150 chrome moly vanadium steel in a heavy profile and chambered in .300 Blackout, with a 1:8 twist rate suited to a wide range of bullet weights in this cartridge. It is finished in Parkerized black, a matte, corrosion-resistant treatment that gives it a clean, uniform look. The barrel runs a pistol-length gas system through a micro low-profile gas block sized for a .750-inch barrel. At the muzzle, 5/8x24 threads carry the included AR-15 TPI GI birdcage flash hider.
Upper Receiver and Handguard
The upper receiver is machined from 7075-T6 aluminum with M4 feed ramps and an anodized finish, giving it a hard, wear-resistant surface that holds up to regular handling. It is paired with a 7-inch black aluminum M-LOK handguard with a partial Picatinny top rail section, which gives the builder a short stretch of rail for an optic or backup sight and M-LOK slots for lights, grips, handstops, and other accessories.
Bolt Carrier Group and Charging Handle
The included complete bolt carrier group is rated for 5.56, .223, .300 Blackout, and .350 Legend, with a carrier machined from 9310 alloy steel and finished in Nitride, a surface treatment that adds hardness and corrosion resistance and helps the carrier stand up to repeated cycling. It is paired with a mil-spec quality M4 charging handle, completing the upper so it is ready to be matched with a compatible lower receiver.
Buffer System and Brace
The kit includes a mil-spec heavy-duty six-position buffer tube and a 3-ounce buffer. An SB Tactical SBA3 adjustable pistol stabilizing brace in black polymer is included and slides onto and adjusts along the mil-spec buffer tube used in this build.
Compatibility
This kit is built for AR-15 lower receivers and .300 Blackout builds. Lower parts kit, pistol grip, recoil spring, castle nut, and end plate inclusion, as well as free-float configuration and forward assist and ejection port door configuration, were not supplied with this listing and should be confirmed before purchase.
Follow all manufacturer instructions and safe handling practices.
Ensure compliance with all applicable federal, state, and local laws.
