I've used Mercury Quicksilver carb cleaner to get my varmint rifle bores squeaky clean. It used to be popular among bench rest rifle shooters, and was recommended by Warren Page. Lately I've been using Shooters Choice when I need a strong bore solvent. I'm not sure if the Quicksilver is still available or if the formula is the same. I think Stan is a Mercury engine guy, and he might know.
Plain old hot water is all I need for cleaning black powder guns since I switched to using T/C Natural Lube . After drying, I then give the bore a thin coat of the same bullet lube.
Many carb cleaners don't seem to be as potent as they used to be. I've found Wynn's is still pretty good for hosing down barrels before rust bluing.
