Tried to get Gunslick today but the LGS didn't have any so I got some Sweets 7.62.
Surprisingly, while the Sweets did remove some more copper it was nothing like the amount I was getting when using Hoppes.
I'm much happier now, but a bit disappointed with Marlin's idea of button rifling (this is a JM Marlin, not a Remlin). This is surprising after the Marlin marketing boys made such a big deal about the button rifling when these rifles first came out.
For what it's worth, I managed to take better pics this time round. In doing so I noticed that with the wrong settings (as per the original pics) the rifling appears to be more coppery than it actually is.
I hope to get some rounds down range this weekend and see if the accuracy, or at least consistency, has returned.