Trying to break in your already broken-in rifle is detrimental. A barrel in 7mm mag is pretty much broken in after the first 50 rounds. You'll cut the lifetime of the barrel by using any abrasive compounds like JB Paste.
Once copper is cleaned out by using something like Butch's, future fouling may be minimized by:
1. Not using all-copper bullets. Gilding metal bullets foul less.
2. Using flat-based bullets for target shooting because they obturate better, sealing off super-hot gasses that cause fouling by liquidizing jacket material, which condenses on the relatively cool bore surface.
3. Try both very slow-burning powders and moderate burn rate powders recommended for the cartridge. Some slow-burn powders may not cause the bullet to deform as quickly to adequately seal the bore. (We've found that to be the cause of leading in revolvers using hard-cast handgun bullets.)
Good luck with your fouling problem. You certainly don't have any accuracy problems!!!
