Remove the lock. If it's flint lock , plug the touch hole. Pour warm water down the muzzle and wait a few min's. Dump the water out ,and repeat. Let sit for a couple mins. , Dump ,and run some patches down and back. Might spray a little WD in followed by some more patches. No need for detergent , soap , Phosphates are bad for the barrel steel . They didn't have soap on the frontier.
Percussion lock...........Let the perc. hammer down on the nipple with a piece of cloth on it. Most percussion drums have a clean out screw on the side. Unscrew the drum clean out screw all but a thread or two. Pour warm water in the barrel , allow to soak a bit. Put patch on the ramrod , remove the clean out screw from the nipple and push the water out of the bore through the nipple clean out screw hole. .........Repeat a couple times Run some patches throught the bore with a shot of WD so the patches don't stick in the bore. When all is clean and dry, ........done. Put some rust proofing oil in the bore and put the rifle muzzle down on a rag , and check in a couple days. oldwood