Davidson Defense Tunnel Scout 18-inch Mid-Length-Gas 1:24 .450 Bushmaster AR-15 Freefloat Tubular M-Lok Handguard Rifle Full Build Kit

Tunnel Scout 18-Inch Mid-Length-Gas 1-24 .450 Bushmaster AR-15 Freefloat Tubular M-LOK Handguard Rifle Full Build Kit

This is an AR-15 full build kit chambered in .450 Bushmaster, centered on an 18-inch HBAR 4150 CMV steel barrel with a phosphate finish and a 1-24 twist rate purpose-built for the .450 Bushmaster chambering. The Panhead billet upper receiver with a widened .458 ejection port cut anchors the front end, paired with a 15-inch tubular M-LOK aluminum handguard with a suppressor ready 1.77-inch internal diameter that wraps the barrel and gas system along the freefloat forend. A .458 SOCOM and .450 Bushmaster compatible bolt carrier group and an M4 Mil-Spec charging handle complete the upper side. The lower completion package covers the full internal lower component group, a Mil-Spec heavy-duty 6-position buffer tube, a matched carbine buffer and recoil spring, and a full rear hardware group. An AR-15 Ranger stock in black with an A-frame style profile, integrated QD mounts, and Mil-Spec carbine buffer tube compatibility closes out the rear end. Everything above the lower receiver is addressed in one kit. Lower receiver not included.

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 tubular M-LOK aluminum handguard, suppressor ready, 1.77-inch internal diameter
• .458 SOCOM and .450 Bushmaster compatible bolt carrier group
• AR-15 M4 Mil-Spec charging handle
• Complete Mil-Spec AR-15 lower parts kit
• Mil-Spec heavy-duty AR-15 6-position buffer tube
• Standard AR-15 carbine buffer, 3 oz.
• Standard AR-15 carbine recoil spring, made in the USA
• AR-15 M16 Mil-Spec receiver end plate
• AR-15 carbine castle nut
• AR-15 Ranger stock, A-frame style, integrated QD mounts, Mil-Spec carbine buffer tube compatible, black
• KAK .458 compensator, 5-8x32 thread pitch
• Black 5-8-inch crush washer

Perfect For

• AR-15 builders who need everything above the lower receiver for a .450 Bushmaster build
• Shooters pairing this kit with an existing stripped or complete AR-15 lower receiver
• Builders who want a fully matched .450 Bushmaster component set with stock included in one kit

Upper Assembly

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. The 15-inch tubular M-LOK aluminum handguard surrounds the barrel and gas system along the freefloat forend with a suppressor ready 1.77-inch internal diameter and M-LOK slots along the handguard body, keeping the front end clean and accessory-ready while retaining clearance for suppressor use under the handguard.

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 component set specific to the .450 Bushmaster chambering.

Lower Completion Components

The complete Mil-Spec AR-15 lower parts kit covers the full internal lower component group, including the fire control group, magazine catch, bolt catch, and all associated pins and springs. The Mil-Spec heavy-duty 6-position buffer tube, standard AR-15 carbine buffer at 3 oz., and standard AR-15 carbine recoil spring made in the USA form the buffer system at the rear of the lower. The AR-15 M16 Mil-Spec receiver end plate and AR-15 carbine castle nut lock the buffer tube down cleanly at the rear of the lower receiver. The AR-15 Ranger stock in black closes out the rear end with an A-frame style profile, integrated QD mounts for sling attachment, and Mil-Spec carbine buffer tube compatibility that pairs directly with the included buffer tube.

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 kit. 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. Lower receiver not included.