AT3™ AT-15 SPEAR XL Billet Builder Set

Transform your AR build with the suppressor-ready AT3 SPEAR XL Builder Set. This complete kit pairs our billet upper receiver with the SPEAR XL M-LOK handguard system, featuring a generous 1.74″ internal diameter that accommodates most suppressors while maintaining full M-LOK compatibility.

The 6061-T6 aluminum construction and steel barrel nut provide rock-solid durability while keeping weight to a minimum. Choose between 12″ and 15″ lengths to match your build requirements, with finishes available in classic black anodized, FDE, or ODG Cerakote to perfectly match your other AT3 components.

To get your rifle together, start with a lower parts kit, a buffer kit, a barrel of your choice, bolt carrier group, and charging handle. And as always, the pistol grip and stock that fits you best. If you’re looking for an even more robust, quad rail handguard, check out the AT-15 Quad Rail Builder Set. If you’re looking for more specific building needs, you can always choose a Stripped AT-15 Lower, or AT-15 Lower and Upper Set.

Durable Construction and Finishes

• Forged 6061-T6 billet aluminum construction for tried-and-true toughness that won’t let you down
• Cerakote in FDE, ODG, or a classic black anodized finish resist scratching and wear over time
• Rigid 7075-T6 aluminum barrel nut provides the support your handguard needs for maintaining zero

Customizable with Cerakote

• Compatible with all mil-spec AR-15 components and numerous upgrades like triggers, pistol grips, safety selectors, and more
• Color coordinate your builds with AT3 parts – we use the same Cerakote colors for all finishes we offer on all AR parts
• Attach accessories using the M-LOK system at 3, 6, and 9 o’clock position, plus a full length picatinny top rail!

Available Finishes

• Black: Type 3 Hardcoat Anodized
• Flat Dark Earth: H-267 Magpul® Flat Dark Earth
• OD Green: H-232 Magpul® OD Green
• Pink: H-224 SIG™ Pink
• Burnt Bronze: H-148 Burnt Bronze
• Tungsten: H-237 Tungsten
• Titanium: H-170 Titanium
• Red: H-167 USMC Red

What’s Included

• AT3 AT-15 Stripped Lower Receiver
• AT3 Slick Side Upper Receiver
  • Includes Black Dust Cover
• AT3 SPEAR M-LOK Handguard
  • 5 Slot M-LOK Rail Section
  • Barrel Nut
  • Barrel Nut Wrench
• AT3 Enhanced Trigger Guard

Specifications

• Lower Receiver
  • Platform: AR-15
  • Material: Forged 7075-T6 Aluminum
  • Markings: “Cal Multi”, Pictogram Safety
  • Compatibility: Works with standard AR15 components and magazines
  • Weight: 8.35oz
• Upper Receiver
  • Material: 6061-T6 billet aluminum
  • Weight: 7.1 oz
  • Feedramps: M4 Feedramps
• Handguard
  • Handguard Material: 6061-T6 Aluminum
  • Handguard inside diameter: 1.35”
  • Barrel Nut Material: 7075-T6 Aluminum
  • Barrel nut inside diameter: 1.02” (compatible with barrels up to 1” diameter)
  • Weight
    • 12″ Handguard – 10.9 oz
    • 15″ Handguard – 11.9 oz
• Trigger Guard
  • Material: 6061-T6 Aluminum

FAQ

Is this lower Mil-Spec?

The AT-15 uses 7075-T6 aluminum construction, and is available in a type 3 hardcoat anodized finish, which are mil-spec. The AT-15 also accepts all mil-spec AR-15 components. Most triggers, pistol grips, lower parts, buffer tubes, and upper receivers will have no issue fitting into this receiver. With the Cerakote options, the thickness of finish in some areas may make the fit a bit tighter.

What is Cerakote?

Cerakote is a ceramic paint and adheres to polymer and metal very well. Since the the lowers are painted, some wear marks may be seen on areas of heavy use. AT3 doesn’t warranty against Cerakote inconsistencies or the wearing of coatings. Our parts are Cerakoted using the official Cerakote colors.

NOTE: Due to the circular shape of the SPEAR XL handguard, the Magpul Gen 2 MBUS Iron Sights are not able to slip onto the top Picatinny rail. However, the Magpul Gen 3 MBUS and other iron sights will fit onto the SPEAR XL with no issue.