I tend to agree with MCH here in terms of back boring the entire barrel. From your comments, it seems to me you are trying to repair and stop pitting in the barrel. The latter should be done, removing as little steel as possible as otherwise the pitting will get worse over time.
Were it mine, I’d send it to Art’s Gunshop to have this done, and a thorough inspection for any other damage or corrosion.
https://artsgunshop.com/
