Montana Extreme and Hoppes#9 The ammonia in the Montana is great on copper. Both are about equal for powder fouling. Follow either with lots of dry patches and then a light swab of CLP.
For me and my 2 cents I would suggest Tetra Gun and Copper Solvent. It does cost a little more than most bore cleaners but I have found it the best in cleaning my Rem. 870 Police with VCS barrel. The ones talked about here are very good but for my dollars I'll go with Tetra Gun and Copper Solvent.
Stay Safe All.