I asked this very same question on another forum the other day about a non S&W stainless revolver. The answers were very similar to the ones posted here.

I haven't tried it, but someone else suggested white vinegar. BIG CAVEAT, however: according to them, this technique will be ruinous to any blued finishes. So if your gun has any blued surfaces, forget it. And I wouldn't use this method in the proximity of any other guns that have blued finishes. But it sounds like a very low cost way to care of the problem.