Hi. Have you heard of Galvanic Corrosion? It's worth a Google..
I think it might be a bit to late to clean that barrel.
Removing the copper now, after 15 years, is sure to exposed pitting caused by GC.. Exposed pitting will result in bullet deformation.
This is a classic situation that supports the old wife's tail. You'll need a few rounds down to cover the exposed pitting.
Whereas, regularl cleaning, to remove copper, would have prevented Galvanic Corrosion (pitting) in the 1st place.
M