+2 on Mr. Berg's excellent discourse.

On Stainless Steel guns I have used Mother's Metal polish, Flitz as well as Lead away cloths to remove the powder and Lead stains on the cylinder holes; but on Nickel I use Mothers or Flitz occasionally. Most polish has some abrasive in it which with repeated use may thin the Nickel finish. So if you shoot a Nickel plated gun a lot, just live with the staining. If you are readying a "Safe-queen" for storage clean it up with mothers or flitz and then protect it with Renaissance Wax. That is the way I do it.

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Revolver luvin' Mountaineer