The San Tan Tactical STT-15 PILLAR is a billet AR-15 upper receiver in 5.56 NATO and .223 Remington (San Tan Tactical part no. STT-PILLAR-1). San Tan Tactical set out to build the lightest billet upper available, cutting it from a single block of 7075-T651 aerospace aluminum and using 3D CAD modeling to remove material wherever it did not add strength. The distinctive receiver truss pockets are the first thing people notice. It comes with M4 feed ramps, a shell deflector and a flat-top Picatinny rail, which makes it a solid foundation for a lightweight carbine or optic-equipped build.

Key Specifications

• The caliber is 5.56 NATO and .223 Remington, the standard AR-15 chamberings.
• The receiver is cut from billet 7075-T651 aerospace aluminum, which gives strength without extra bulk.
• San Tan Tactical lists the weight at 8.2 ounces for the upper, a light figure for a billet receiver.
• The aluminum is finished with Type III hard anodize for wear resistance.
• The upper has M4 feed ramps, which help rounds feed from the magazine into the chamber.
• A shell deflector is built in to keep ejected cases clear of the shooter.
• The top is a flat-top Picatinny rail with machined T-markings, making it easy to relocate an optic to the same spot.
• The receiver uses truss pockets that stiffen the receiver while keeping weight down.
• It works with mil-spec AR-15 and M16 components, excluding San Tan Tactical’s proprietary ambidextrous controls.
• The upper carries a lifetime warranty and is made in America.

Frequently Asked Questions

Is this upper a complete assembly? No. It is an upper receiver only, so you add the barrel, bolt carrier group and charging handle to complete the upper.

What calibers can I use it for? It is listed for 5.56 NATO and .223 Remington, and it works with mil-spec AR-15 components.

Is there a rail for an optic? Yes. The top rail is a flat-top Picatinny rail with machined T-markings to help with repeatable optic placement.

Buy the San Tan Tactical STT-15 PILLAR Billet Upper Receiver

Billet uppers usually trade weight for strength, and this one was designed to avoid that trade. It is lighter than most, has a distinctive look, and is built in the USA under San Tan Tactical’s lifetime warranty. Shop more AR-15 uppers and order from our Lubbock, Texas gun shop for fast direct shipping.