As noted, it is about NOT putting grit into your reloading dies. Cases just need to be clean though, factory shiny new is a bonus, curse at times. For years I just rolled my empties in a damp towel. I only loaded 100rds of 357mag a week. Then I went to a dry tumbler, just easy & if you add a polish, it leaves a thin coating that helps in sizing. Wet cleaning is fine, but IMO< they are too clean & really make things more diff during reloading & powder charging on a progressive.

__________________
NRA Cert. Inst. IDPA CSO