Get a set of assorted vaccuum line caps (any auto parts store), a bottle of Hydrogen Peroxide (Walmart or any drug store) and a bottle of white vinegar (Walmart, any grocery store.)
Remove the cylinder, stand the gun up in the sink, and plug the breech with a vaccuum line cap. Pour a 50-50 mixture of vinegar and H2O2 into the barrel. Watch carefully, and don't get the mixture on the stocks, blue, etc.
A gray scum will form. That's the lead -- pour it directly down the drain. Dry and inspect the barrel. Repeat as needed.
Finally, dry thoroughly and oil as normal.