I use CLP to lube and clean, but I want to get a good copper solvent.

Butches Bore Shine is one of the best, use it every time you clean the bore. If you have bad copper fouling use Sweets as nothing is stronger Be careful with the Sweets as it can damage your barrel if left in the bore to long....Follow the instructions to the T and you will be good to go!

have not used it but Sinclair is selling Montana .50 BMG Copper Remover.  They claim it's the strongest on the market, stronger than Sweets.

Sinclair Link

I use shooters choice, works great.  

+1 for the Shooters Choice.  I also have used and like Hoppes Benchrest Coper Solvent.  The Shooters Choice is easier to handle, with a drip top bottle, where the Hoppes is a twist off top and always seems to get knocked over by a gremlin and I loose half the bottle.  And this stuff is too expensive to spill half of it on the floor.  Whatever you use, don't let it sit in the bore long before removing and cleaning out with something else.  And don't wait till it builds up so bad it would take a sledge hammer to get out.  I use copper remover every other range visit.

If it gets REAL bad, you could always make one of those electronic foul out thingies.  I made one myself for just a few bucks and I use it on disaster cases (I collect milsurps).  

Lois

Montana .50 BMG Copper Remover is what I've been using and it does work well.

I've only used hoppes, it works well.

Hoppe's #9 works well if you allow it to soak overnight.If used on every cleaning it tends to keep the copper at a minimal level.Its one of my all time favorite solvents.
For a pure copper solvent the Sweets 7.62,BoreTechs Copper Remover and Butches are at the top of my list.With a overall performance edge going to the BoreTech and Butches as they use buffered ammonia and contains a corrosion inhibitor.That being said the Sweets is the strongest of the bunch...so if your in a hurry its the one to use.Just follow the directions.
The BoreTech Benchrest is also very effective with the ability to remove copper and powder fouling.The BoreTech bore solvent is another verygood everyday mild copper and very effective powder solvent,its a bit more effective than the Hoppe's #9.
All work IMHO.

Montana Extreme .50 BMG is awesome, even stronger then Sweets 7.62 but safer in the bore for longer periods of time.  Make sure you have nylon bore brushes on hand to apply it, it will quickly dissolve a bronze brush.

I've had good results with both Shooters Choice and Sweets 7.62...but as others have said, don't leave it in the bore more than about 5 minutes. Repeat if necessary.