I agree with Kirby about Tetra Copper Solvent. I started using it about 18 months ago, and found that it still removes copper after Sweets, Butches Boreshine, Hoppes, and a host of others seem to have given up.
I have been using it the last week in cleaning the barrel during the break in, and then load development with the 156 grain Wildcat of my Krieger 7 twist barrel chambered for the 257 Weatherby. Regards, Brian.