Davidson Defense Koschei 18-inch Mid-Gas 1:24 .450 Bushmaster AR-15 Freefloat M-Lok Handguard Rifle Complete Upper Build

Koschei 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 no forward assist design and 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 K style freefloat M-LOK handguard keeps the front end trim and light with 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, no forward assist, .458 ejection port cut
• AR-15 ejection port door assembly
• 15-inch ultra-lightweight minimalist M-LOK handguard, K style, 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 a no forward assist design and a widened .458 ejection port cut, both purpose-built features for the larger case diameter of the .450 Bushmaster chambering that a standard AR-15 receiver 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 K Style M-LOK Handguard

The 15-inch ultra-lightweight minimalist K style freefloat M-LOK handguard surrounds the barrel and gas system along the forend, prioritizing a trim and light front end profile that keeps the overall build balanced on an 18-inch .450 Bushmaster platform. M-LOK slots run along the handguard body for accessory attachment across the forend without adding unnecessary weight or bulk to the front end. The handguard does not include anti-rotation tabs, a design characteristic of this specific unit, and the K style profile gives the forend a distinctive exterior shape compared to standard round or octagonal handguard profiles.

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.

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