CC, you can find reports of barrel damage from solvents containing ammonia, or so the reviewers (they) say. I am not commenting on their veracity as such. I used Barnes CR-10 for years for copper, was always careful to clean it out good and finish with a very light oil patch. It worked well with no damage I know of. Once I saw the studies showing how effective KG-12 is reported to be on removing copper, and it's said lack of damage potential, I went with it. Smells much better too!
That said, I do not clean for copper much at all, especially in my hand lapped custom barrels.