When polishing for rust bluing,generally worn 320 grit(maybe 400 grit)cloth is used(by hand).If the barrels are highly polished with "rouge" on a polishing wheel, the bluing solution won't "bite"(especially on hardened steel).Furthermore, the rusting action of the solution will produce a somewhat matt finish anyway.This is the normally desired finish.Some people may wax/polish rustblued barrels for a shiny finish, not I.
Mike