No commercial bore cleaner will damage the finish. Best to remove the sideplate and disassemble the lockwork for a thorough cleaning and lubrication. It's not that difficult. There is a trick to removing the sideplate without damaging it (mainly don't try to pry it off, although some do it that way). There are YouTube videos showing how to disassemble a S&W. The quick and easy way is to get a can of spray carburetor cleaner solvent and blast everything by sticking the red tube into all openings around the hammer and trigger. Or just soak the whole gun overnight in a suitable container of mineral spirits.