So, you’ve got copper. How do you get rid of it? There are three ways: First, let the bore soak in Shooter’s Choice or Hoppe’s Benchrest, muzzle pointed slightly down, until green gravy collects at the muzzle. (By the way, put a newspaper under the muzzle. Dissolved copper makes fabulous stains). Run another wet patch through, and repeat as needed. This process works most of the time, and does not involve elbow grease, but is very slow. It can take days to get the job done completely, and there are cases of copper fouling where it has no effect at all, and I have no idea why.