I know a couple of ways to get the black rings off the cylinder front of a stainless revolver. Both involve a little, but not too much elbow grease, and take a couple of minutes.
Generally, I brush them out with a solvent soaked bronze brush. The bronze is softer than steel and won't erode it.
Or, I use a lead removing cloth. There are several makes out there and they all seem to work. I'm using a Birchwood Casey cloth at the moment, it does the job with little fuss (the cloth, when cut into strips, also does an excellent job of cleaning the bore and chambers).
Whatever you do, however, do NOT use either of these techniques on a blued gun. The bronze brush will erode blueing and the lead removing cloth will also take off blueing. I clean my blued guns with a lead removing cloth that is marked "safe" for blued guns which I purchased from Brownells.