I am of the borescope persuasion.
I am not saying this is your issue, but a couple of my friends and I have turned half a dozen bad older rifles into much better guns with a LOT (a hell of a lot) of bore cleaning. And a 7 Rem Mag was the one that showed the most dramatic improvement. It was a BLR and with 4 sessions of scrubbing it went from a plus 4 inch to a 1.25 inch gun.
It is incredible how much fouling can build up in a magnum rifle barrel.
Again, I don't say this is your problem, but sometimes it is the problem.
