I'm not slamming Hoppes, it cleans as well as most things out there when it comes to powder fouling. There is hard packed carbon in bores that most folks dont know is there. Its packed in place by each round fired packing the carbon from the previous round. After testing dozens of bore cleaners and clp products I found NONE of them removed this hard packed carbon except those with abrasives. The best I found was Flitz liquid/bore cleaner, the green stuff. It performed best in my tests but still had a hard time getting out all of it. In the end I added Iosso bore paste to my flitz, 1/2 tube per 8oz bottle and it was a game changer for me. I've never had copper issues with Hammers. In fact I have to look very hard to see any copper and usually its a very faint transparent haze and comes out easily. Hope this helps.
I clean out the flitz with Seal 1 which is also one of the best rust preventatives I have found. Just wipe off when done.
Not trying to start a debate here, just stating what works best for me after spending hundreds of $ testing cleaners and lubes.