Get a bronze scrubbing pad, unfold it, cut about a 1" square out of it, and wrap it around a patch wrapped around a smaller nylon brush... nylon brush inside patch inside bronze. Do not let the whole assembly exit the muzzle. Just bring the tip flush with the crown.
It will scour out the lead and leave you with little piles of shavings at the muzzle and breach.
"Chore Boy" pure copper is your friend for heavy lead.
