I agree, that if the 243 is downloaded enough, it won't be a problem, but then again, when will a person know when they have exceeded that point.
I would chance to bet that even a down loaded 243 will have just about the same pressure effects on the frame as a 300 savage will. Just look at the top end pressures of both cartridges. 300 savage maxes out about 10000 cup lower than the 243 maxes out.
NOt arguing, because I also have a 300 savage, but felt recoil is due to the larger projectile being forced through the barrel, even when the 300 savage is operating at lower pressures.