The Cross Machine Tool Ultra Precision Upper Receiver Part# UPUR-1A is the perfect Mate to your UHP-15 lower receiver or would also be a great match with any Mil-Spec lower. The UPUR-1A is machined from Billet 7075 T6 Aluminum unlike the more commonly used 6061. Using the 7075 T6 aluminum gives the UPUR-1A a 65% increase in strength & rigidity over 6061 aluminum receivers. The UPUR-1A is machined on a 5 Axis machining Center to reduce the number of operations/setups required to complete. This machining process allows the highest possible accuracy to be obtained over the traditional 3 or 4 Axis machining method. The UPUR-1A is designed for increased function, performance & to Mfg: Cross Machine Tool Co.