Use some penetrating oil like "Liquid Wrench" or " BreakFree", or "Kroil" to soak the bore and reduce the rust you find. Then polish the bore using a product called JB bore cleaner. If you don't have it locally, Use a dampened patch on your jag( 2 if needed to get a tight fit) and put toothpaste on the patch. Run that back and forth in the barrel to polish the lands. Use new cleaning patches if you find the one in use turning black. The Black is iron oxide and oil.
The Grooves may still be rough, and the best way to remove the rust there is by pouring a lead "LAP" to run up and down the barrel with lapping compounds. However, most people are not set up to do lapping, or simply don't want to try it, without some experienced help standing by! :shocked2:
There is a process called " Fire-lapping" Where lapping compound and oil are put on a patch wrapped around a ball. The combination PRB is then loaded down on to a powder charge- usually somthing less than what you might fire for target practice-- and the ball and patch are fired out the barrel. This will get rust out of the grooves, after a few shots, provided you are using the correct thickness of patch fabric to fill those grooves. But, any rust located in the barrel Behind where the PRB is seated will remain in the barrel. Only removing the Breechplug and lapping the full barrel will get all the rust out. That doesn't mean you won't have pitting left in the barrel, however.
Pits require you to spend extra time cleaning the barrel to get the residue of burned powder OUT of the pits. otherwise, such residue will attract water( Moisture) and you will see more rust, even under some of the oils, or preservatives used to protect the rest of the barrel from rust. With pitted barrels, let the barrel SIT some place, full of soap and water, for about and hour. The soap will get the carbon residue out of the pores and pits for you.
Then you can flush both the residue and the soap out of the barrel before drying the barrel and then lubing it to keep new rust away. Use tepid water( warm, NOT HOT!) to clean barrels. It works just as well as HOT WATER will, but you won't burn your hands. :hmm: :thumbsup: