+1 on Flitz. I ran an 8" Silver Snake for a dozen years in competition shooting, with cast. Do not use a copper solvent on the gun and leave it on the gun when stored.....real Nickel plate is copper over steel, with nickel plate on top of the copper, a chip, crack or scratch will expose the copper to the solvent. Good idea to pull the grips, remove all of the oil under the grips, then wax the nickel plate under the grips, put grips back on.
Before you try to polish anything, make very sure the finish is not satin nickel, it will not polish well.