In the old days
you'd just "freshen" the barrel... Nowadays, most people say contact Bobby Hoyt !! Depends on how bad the rust\pits are and if it will clean, to load and shoot decently ' as is'?
Not trying to be that guy??? But have you tried to clean it up?? A green or maroon scotchbrite, worked through the bore, will tell you where your at I'd think??? I have wound some 4\0 steel wool onto an
undersized cleaning brush and worked out the junk my nephew left behind in my St Louis hawken after he borrowed it
Let us know and maybe one of the others will chime in with a solution...
Oh and if you are not worried about the outside patina??? Get some PVC tubing ( long enough ) and an end cap.. glue them together and soak the barrel in Evaporust!!! Soak about 2 hrs, and then run a brush through the un-breached barrel.. the crud shud come out fairly easily.. soak, brush repeat... Rinse and oil... Evaporust attacks the oxides ( rust\bluing\browning ) but doesn't harm the base metal.. then you should really be able to see how bad the pitting is??
Ok, got long winded
Respect Always
Metalshaper\Jonathan