I use mag primers with the slower powders. Not sure, but I think Don Bowers recommended it for his wildcats and the slow powder.
Drop back to a faster powder, like 414, 4895. 748. The case will not be full but the accuracy may be there anyway.
My 7-08 likes 760, I have not spread the sheet, but the barrel is clean.
You are in the fun part, once you find the most efficient load it is time to trade the barrel.