There are several several dry lubes that come to mind. I use them for handloading.
Mica, a white powder
Molybdenum disulfide (Moly)
Graphite powder

Moly is especially slick. It's a black powder that clings pretty well. It's used to coat bullets and barrels to make them more slick, i.e.increase velocity. I have a Teflon rail on my Terminator so needs no 'slicking' but may just try it on my Excal.