we *try* to make sure there are zero sanding marks in our finished pieces. So we go a little overboard sometimes. I'd think you could go from 100 to 150 and then possibly 220 then start with the wet sanding grits after that. It's difficult to tell what the end result will be but when you polish metal you've sanded with 100 grit, I guarantee scratches will be all over it. Since you jumped grits all the way to 320, it only sanded the top of the scratches and left the deepest part still there.
