Depending on the type of finish you're looking for. I use wet or dry sandpaper. A brushed metal finish from the factory is usually 320 to 400 grit. Some stainless steel guns have a bead blasted finish. In which case you can either polish them out or leave well enough alone. For a mirror like finish similar to chrome or nickel plating. I start with 220 and work my way up to 2000. Obviously before starting the guns have to be taken completely apart and thoroughly cleaned when you're done and then put back together.