San Tan Tactical STT-15L Lite PILLAR Billet Upper Receiver

San Tan Tactical machines the STT-15L Lite PILLAR upper from a single billet of 7075 aluminum and then removes weight from it in two ways. The forward-assist housing is deleted outright, and the receiver walls carry San Tan's truss pockets, which cut mass while keeping the structure rigid. The result is 6.9 ounces, which San Tan measures against the 8.2-ounce standard STT-15 upper.

That weight is the point of the receiver. Billet uppers usually cost weight for the privilege of a machined profile: the CMT UPUR-2 is a slick-side billet body at 8.2 ounces. The STT-15L instead lands at the same 6.9 ounces as Aero Precision's forged receivers, so a builder chasing a light upper no longer has to give up billet machining to get there.

The shell deflector stays, the feed ramps are cut to M4 dimensions, and the top rail carries machined T-markings for repeatable optic placement. San Tan documents anti-rotation tab and pin clearance for a range of handguards including the Noveske NSR, so the receiver is not locked to a proprietary rail. Finish is Type III Class II hardcoat anodized black, and the receiver ships stripped, so the barrel, handguard, bolt carrier group, and charging handle are separate purchases.