Davidson Defense Manticore 18-inch Mid-Gas 1:24 .450 Bushmaster AR-15 Quad-Rail Rifle Upper Build Kit

Manticore 18-inch .450 Bushmaster AR-15 Upper Build Kit

The Manticore is built around an 18-inch heavy .450 Bushmaster barrel, finished in phosphate, paired with a "Panhead" billet upper receiver machined without a forward assist and featuring an enlarged, .458-compatible ejection port. It pairs a 15-inch free-float quad-rail handguard with a KAK .458 compensator at the muzzle, running on a mid-length gas system. BCG and charging handle are not included, leaving the buyer to supply those components separately.

Key Features

• 18-inch .450 Bushmaster heavy barrel, 1:24 twist, phosphate finish
• Mid-length gas system with micro low-profile steel gas block
• "Panhead" billet upper receiver, no forward assist, enlarged .458-compatible ejection port
• 15-inch free-float quad-rail handguard, full-length Picatinny
• KAK .458 compensator
• BCG and charging handle are not included.

Barrel and Gas System

The barrel runs 18 inches long, chambered in .450 Bushmaster and built from 4150 chrome moly vanadium steel with a phosphate finish and HBAR profile. It carries a 1:24 twist rate. Gas cycles back to the action through a mid-length system, running a stainless steel gas tube and a micro low-profile steel gas block sized to a .750-inch diameter.

Upper Receiver and Handguard

The upper receiver is a "Panhead" billet unit machined without a forward assist and featuring an enlarged .458-compatible ejection port, sized to accommodate this larger-diameter cartridge, with its door, rod, and spring installed. Over the barrel sits a 15-inch free-float quad-rail handguard with a full-length Picatinny rail running along its top, finished in black.

Muzzle Device

Capping the muzzle is a KAK .458 compensator, threaded to match the barrel's 5/8x32 pattern and secured with the included 5/8-inch black crush washer.

Follow all manufacturer instructions and safe handling practices.

Ensure compliance with all applicable federal, state, and local laws.

BCG and charging handle are not included.