Details
Thunderbird 18-Inch Mid-Gas 1-24 .450 Bushmaster AR-15 Freefloat M-LOK Handguard Rifle Complete Upper
This is a complete AR-15 upper chambered in .450 Bushmaster, built around an 18-inch HBAR 4150 CMV steel barrel with a phosphate finish and a 1-24 twist rate specific to the .450 Bushmaster chambering. The Panhead billet upper receiver with a widened .458 ejection port cut anchors the front end with a profile purpose-built for the larger bore diameter of this chambering. The 15-inch ultra-lightweight minimalist rail freefloat M-LOK handguard keeps the front end trim and light with a partial top rail for optics and accessory mounting and M-LOK slots along the forend body. A .458 SOCOM and .450 Bushmaster compatible bolt carrier group and an M4 Mil-Spec charging handle complete the upper component set.
Key Features
- .450 Bushmaster chambering, 18-inch HBAR 4150 CMV steel barrel, phosphate finish
- 1-24 twist rate, 5-8x32 thread pitch
- Mid-length gas system with mid-length stainless steel gas tube
- Micro low-profile steel gas block, .750 inch
- Panhead billet upper receiver, .458 ejection port door cut
- AR-15 ejection port door assembly
- 15-inch ultra-lightweight minimalist rail freefloat M-LOK handguard, partial top rail, no anti-rotation tabs
- .458 SOCOM and .450 Bushmaster compatible bolt carrier group
- AR-15 M4 Mil-Spec charging handle
- KAK .458 compensator, 5-8x32 thread pitch
- Black 5-8-inch crush washer
Perfect For
- AR-15 builders pairing a complete .450 Bushmaster upper with an existing lower
- Shooters adding an 18-inch .450 Bushmaster upper to an AR-15 lower they already own
- Builders who want a BCG and charging handle included with a purpose-built .450 Bushmaster upper assembly
Upper Receiver and Barrel
The Panhead billet upper receiver anchors the front end with its widened .458 ejection port cut, a purpose-built design feature for the larger case diameter of the .450 Bushmaster chambering that a standard AR-15 ejection port does not accommodate as cleanly. An AR-15 ejection port door assembly is included as part of the upper. The 18-inch HBAR 4150 CMV steel barrel brings a phosphate finish and a 1-24 twist rate to the .450 Bushmaster chamber, threaded at 5-8x32, a thread pitch specific to this bore diameter. The mid-length stainless steel gas tube and micro low-profile steel gas block at .750 inch run a well-matched mid-length gas system along the barrel for the 18-inch profile, keeping the gas timing appropriate for this barrel and chambering combination.
Ultra-Lightweight Minimalist Rail Freefloat M-LOK Handguard
The 15-inch ultra-lightweight minimalist rail freefloat M-LOK handguard surrounds the barrel and gas system along the forend, prioritizing a trim and light front end profile that balances well on an 18-inch .450 Bushmaster build. A partial top rail provides a solid mounting position for optics and accessories at the front end where they matter most, while M-LOK slots along the handguard body keep the rest of the forend clean and accessory-ready without adding unnecessary weight or bulk. The handguard does not include anti-rotation tabs, a design characteristic of this specific unit.
Bolt Carrier Group and Charging Handle
The included bolt carrier group is compatible with both .458 SOCOM and .450 Bushmaster, addressing the platform-specific BCG requirement for this bore diameter that a standard AR-15 bolt carrier group does not meet. The M4 Mil-Spec charging handle pairs with the BCG inside the upper receiver to complete the upper interior. Together these two components finish the upper side with a fully matched and chambering-specific component set that gives this complete upper everything it needs to drop onto a lower.
Muzzle Device
The KAK .458 compensator threads onto the 5-8x32 muzzle end of the barrel, a thread pitch and caliber designation specific to the .450 Bushmaster bore diameter. The included black 5-8-inch crush washer seats at the barrel shoulder and completes the muzzle hardware for this upper. The KAK .458 compensator is a purpose-built muzzle device for this chambering and thread pitch combination.
Follow safe handling and manufacturer instructions. Ensure compliance with all applicable federal, state, and local laws.
