A couple of years ago, I cleaned up an old-ish Getz .54 caliber swamped barrel that had been given to me many years before. The bore had a fine covering of orange rust throughout, but no obvious pitting. Don Getz, shortly before his death, posted here that it would probably be salvageable. Here is his response:
"Here's how I would scrub the bore using scotchbrite. I would use either the green stuff
that you can get in a grocery store, or maroon from whereever. You said it was a 54
I believe. Cut a piece about 2" x 3". Tape the 3" side to a 3/8" ramrod, wrap it
tightly around the rod, and push it in. If it's too tight, trim it with a scissors until it wil
go in the bore. I normally used the stuff dry, but you can add some oil. It will not
remove metal, but you will be amazed at how well it will shine that barrel.......Don"
I did as he suggested, going through the bore a couple of hundred times with the Scotchbrite, and the bore cleaned up very nicely and shoots well. Again, this was fine surface rust only with no pitting.
Gregg