I usually don't have a problem with leading in my cap and ball revolvers. I shoot mostly balls and use a well-lubricated felt wad between ball and powder.
But once a year I use a bunch of tight patches, well saturated with Iosso Bore Cleaner (comes in a tube, consistency of toothpaste) or JB Bore Cleaner (in a little screw-top jar, and is the consistency of putty).
Either of these substances, thoroughly worked into the patch, then the patch a tight fit in the bore, will do. Work the patch back and forth at least a dozen times, before removing.
This annual treatment removes what little lead may be in the bore and smooths the bore a bit too. The Iosso or JB have very, very fine abrasives in them that are harmless to the bore but will grab any fouling and push it out.
It's good stuff.
During regular cleaning, I run a bronze brush through the bore a dozen times or more, mostly to loosen any fouiling but I suppose it gets a little lead too. I never really see any leading in the bore, though.