Davidson Defense Whitecap w/SBA3 Brace 10.5-inch Carbine-Gas 5.56 NATO AR-15 Drop-In Quad-Rail Handguard Pistol Full Build Kit

Whitecap w/SBA3 Brace 10.5-inch 5.56 NATO AR-15 Full Build Kit

The Whitecap w/SBA3 Brace is built around a 10.5-inch front sight base barrel chambered in 5.56 NATO, paired with a 7075-T6 aluminum upper receiver. It pairs a 7-inch M4 carbine-length drop-in quad-rail handguard, finished in black, with an A2-style front sight base and an A2 GI birdcage flash hider at the muzzle. A complete bolt carrier group, Mil-Spec charging handle, complete Lower Parts Kit, carbine buffer-system components, and an SB Tactical SBA3 adjustable pistol stabilizing brace round out the rest of the build. The lower receiver is not included, leaving the buyer to select and supply that component separately.

Key Features

• 10.5-inch 5.56 NATO barrel with front sight base configuration
• Carbine-length gas system with stainless steel gas tube
• 7075-T6 aluminum upper receiver with M4 feed ramps
• 7-inch M4 carbine-length drop-in quad-rail handguard, four-sided Picatinny rail
• A2-style front sight base, USA-made steel components
• A2 GI birdcage flash hider, 5.56/.223 compatible
• SB Tactical SBA3 adjustable pistol stabilizing brace included
• Complete Mil-Spec Lower Parts Kit and carbine buffer-system components included
• Lower receiver is not included.

Barrel and Gas System

The barrel runs 10.5 inches long, chambered in 5.56 NATO and built in a front sight base configuration rather than a low-profile gas block setup. Gas cycles back to the action through a carbine-length system, running a carbine-length stainless steel gas tube. This barrel length paired with a carbine-length gas system gives the build a shorter dwell time than a typical mid-length or rifle-length setup.

Front Sight Base and Upper Receiver

Mounted on the barrel is an A2-style front sight base, fitted with USA-made steel components including the front sight post, plunger, and spring. The upper receiver is machined from 7075-T6 aluminum with an anodized finish, cut with M4 feed ramps for smooth feeding and fitted with a standard AR-15 forward assist assembly. The ejection port carries a standard .223/5.56 door with its rod and spring installed.

Handguard

The handguard is a 7-inch M4 carbine-length drop-in design finished in black, built around a four-sided Picatinny quad rail rather than a slimmer M-LOK profile. It mounts using a Colt AR-15 delta ring assembly, giving it the classic two-piece drop-in fit rather than a free-float clamp-on design.

Muzzle Device

Capping the muzzle is an A2 GI birdcage flash hider, compatible with both 5.56 NATO and .223 Remington. It threads onto the barrel's 1/2x28 pattern and is secured in its final timed position with a 1/2-inch black crush washer.

Bolt Carrier Group and Charging Handle

A complete AR-15 bolt carrier group is included, made in the USA and listed for use across 5.56 NATO, .223 Remington, .300 Blackout, and .350 Legend. That broader listing describes the BCG itself; the barrel and chambering on this build remain 5.56 NATO. A Mil-Spec AR-15 M4 charging handle rounds out the upper's operating components.

Lower Parts Kit and Buffer System

A complete Mil-Spec AR-15 Lower Parts Kit covers the fire-control and lower-control internals needed once a lower receiver is on hand. Behind it sits a Mil-Spec heavy-duty six-position adjustable buffer tube, holding a standard AR-15 carbine buffer weighing 3 ounces and a standard USA-made recoil spring. A standard castle nut and Mil-Spec AR-15/M16 receiver end plate secure the buffer tube assembly to the lower.

Stabilizing Brace

Capping off the rear of the build is an SB Tactical SBA3 adjustable pistol stabilizing brace finished in black. It's built for Mil-Spec carbine buffer tubes, matching the six-position buffer tube included with this kit.

Follow all manufacturer instructions and safe handling practices.

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

Lower receiver is not included.