I polished the cylinders of my 357max many years ago when I had a similiar problem. I used a dowel a few sizes smaller and wrapped some 600 grit paper til lightly snug and used a drill to slowly work from the back to the throats, careful not to taper the throats or you may create an accuracy problem. If you saved one of your hard to eject brass; you could use as a guide to check your progress, that's what I did and when it slid in and out smoothly, I quit, haven't had a problem since.