Heres a copper solvent some high power shooters used to make. 1 gallon 28% ammonia 2 tablespoons hydrogen peroxide and hang a length of copper wire in it for a couple days. It will turn a very pretty blue color Hence the name Blue Goo. I used to remember the transformation that took place. But it supposedly was a great copper remover. I never like amonia for barrel cleaning so didnt use it.