I just got this tip from the range master at our local range who shoots PPC regularly and is a High Master marksman with a revolver. I tried it, and was amazed at how well it cleaned the cylinder on a model 617 (10 shot) that had over 3000 rounds of dirty .22 lr through it without a cleaning. The result was a cylinder face (in fact, the whole badly fouled hard-to-clean cylinder was clean for that matter) that looked literally BRAND SPANKING NEW, with NO SIGN of carbon ring whatsoever.
Take a small, wide mouthed canning jar ( I used Kerr brand. I think they are about 12 oz. in size) and fill it 3/4 full of your favorite gun solvent. I used Butch's bore shine, but was told that Hoppe's #9 works just as well.
Remove your cylinder from the frame (easy to do) and drop it in the solution. Let it stay there submersed for 3-5 days.
When you remove it, most of the fouling will have fallen right off. With just a light low-effort scrubbing with a bronze brush, the cylinder will look BRAND NEW!
There was no discoloration or undesireable side affects. I sprayed the parts down with some Rig rust protectant and removed the excess with compressed air, wiped clean, and stored it away.
The canning jar will keep the dedicated solvent sealed for future treatments.
This is supposed to work on blued guns just as well, and with no side effects to the blueing or any discoloration.
Try it!