If it's a 12 gauge you can use a power drill and an automotive brake cylinder hone (with a couple of drill bit extensions wrapped in vent tape at the junctions) to clean out the inside of the barrels. Make sure you use lots of oil inside the barrels when you spin the hone. After you've honed the barrels take a cleaning rod tipped with a 12 gauge wire brush, wrap it in steel wool and dip it in automotive polishing compound (the orange paste), next chuck it to your power drill and run it up and down inside the barrels for awhile to polish them. When you're done the barrels will be shiny and bright inside again.
Steve
