Okay, here is a pic of the barrel before today's cleaning. Below that is a pic of the cleaner I got at the LGS. They had Hoppe's Copper Cleaner in a small bottle, but I opted for this foam.
I used a new bronze brush, a SS tornado type brush, and a brass jag. I let it soak for the recommended time and cleaaned it. When the crust was still there, I repeated the procedure. The first time I got the blue color, so obviously there was some copper in there. But the second time I got no blue.
I tried the regular Hoppe's #9, and then swabbed with patches, and got some black residue out and continued that until it came clean. From the last pic, it appears that the caked build-up is not as heavy. I feel confident in saying that some of it has been removed.
However, at this point I don't think that what remains is copper. It appears to be a carbon/powder build-up....I don't know for sure. It appears pretty black colored.
Sorry for the lighting, but I had to use a flashlight instead sunlight, and it was more difficult to get a good pic.
At this point, I'm going to leave it as-is and shoot it this weekend. I'll clean it after that and see if it comes out. I'm going to order some Sweet's 7.62 and see if that gets the rest of it out of there.
Actually, I might pick up some Seafoam at the automotive store tomorrow and try soaking in that.