The ammonia based copper cutters work, but they use ammonia which can be potentially harmfull to your bore and you for that matter. If you use them as many do go behind them with your regular bore cleaner and then a good gun oil.
I would suggest using Bore Tech's Eliminator. It is safe and cuts copper like nothing I have seen and I have used all of the strong ammonia based products.
For pistol barrels I use Carbon Killer from Slip 2000 for the carbon and Eliminator for the copper and barrels come sqeaky clean under magnification. (bore scope)
http://www.boretech.com/introducing.htm
http://www.boretech.com/product.htm
http://www.slip2000.com/Merchant2/me...tegory_Code=CK
http://www.slip2000.com
M-Pro 7 and Slip 2000 make excellent products for complete gun care.