Lots of good advice here. I'm with Digital Dan...light loads, 50-60 gr of 3F. Cotton twill patches, any patch lube, I am fond of Murphy's Oil Soap/water for repeated shooting, animal fat for days long hunting. Avoid petroleum based products. Patch fit is everything...recover your fired patches, ideally they will be re-useable, no shredding, no burns, no holes. Then you will have achieved top accuracy and consistent velocity. If you have corrosion (different from fouling) of any kind in the bore, a little abrasive paste (JB is too fine) Clover Compound, fine grade, rubbed into your patches, usually 10 to 20 shots is more than sufficient to fire lap the bore. You will find the ramrod pressure, uniform and smooth and undamaged patches will be your indicator of when to stop fire lapping. Personally I am not a fan of abrasive scrubbing with a range rod, no matter how careful, you will bellmouth the muzzle, arguably the most critical portion of the bbl for accuracy.
The Thompson barrels 48 or 66", when fed a proper diet will shoot with any barrel out there, the snooty custom gun makers hate that fact.
