Building the semi autos when I was at S&W we used what i believe was regular 30 wt motor oil, nothing special. Our goal as fitters was to build a gun, get it through the range and not have "repairs" which were guns that did not pass the final range test for a number of reasons from not feeding, slide stop not staying open etc. Any oil was applied and wiped off. The gun should function with a minimum of lubricant.