The San Tan Tactical STT-15 Pillar Billet AR-15 Upper Receiver has innovative weight savings in areas where extra mass isn't needed, and extra strength in areas where it is needed. San Tan's Pillar Upper is CNC machined with the use of 3D CAD modeling software. The Pillar has a new truss system to help distribute weight of longer handguard systems throughout the entire upper receiver instead of putting the entire weight of the handguard on the threads of the receiver. Excess weight has been removed from the the forward assist block and the shell deflector. The result is a billet upper that has a weight of only 8.2 ounces which is lighter than some slick side uppers.