I always remove the barrels from my percussion long guns - one is not a hooked breech so it involves a little more care and effort, but I've not had any problems.
Once upon a time, many years ago, the first time I cleaned my brand new Kentucky rifle, I was afraid to remove the barrel, so I took off the front cap, put the muzzle in a pan with about an inch and a half of hot, soapy water, attached a rubber hose to the nipple, put the other end of the hose in my mouth and proceeded to suck the water up into the barrel. And into my mouth. Really. Yes, I did. Not a pleasant experience. Hey, we were all young once...