suggestions on new 7mm Mag BBL

My 110 in 7 mag chokes up with copper in about 20 rounds. Shoots good ( about 3/4" - 1"MOA) till about a dozen rounds then craps out. By 20 rounds it becomes the worst barrel I have ever worked with. Takes a great deal of work to clear residual copper when cleaned. I have all the stuff to change barrels and reload and I like the round. Has anyone worked with IMR 7977 which is supposed to have copper eliminator formulation? If so what have been you observations. So If that isn't a solution, I am thinking about a decent after market barrel. I would like to get a savage prefit in a heavy sporter contour. Stainless or blued OK. I will probably have the whole kit cerakoted once I prove any new barrel out. Price is always a concern so what suggestions can you provide please. Thanks