I have polished the metal within the bottom of the powder hopper, (as well as cleaning up the rough spots) the inside of the powder tube, the outside of the powder tube including the expander, the powder bar and the slide that it runs in (plus cleaning up any rough spots there too) along with the sizer die. Even polished the primer slide a bit (not sure that actually did anything though). All were polished using a stainless steel polishing compound. Starting off first with a 3M pad.
Oh, and cleaned up the little square opening in the powder bar where the nylon square button sits so it wouldn't grab at all.