His is a totally different situation though Oldtimr. Your 45-70 is big and slow (I like those too) but his is/can be medium weight and still fast. Hunter,,,welcome to the site first off. As to your question, it really has little to do with the weight of the bullet as it does towards the construction of the bullet. Bigger/heavier doesn't necessarily mean tougher. More often than not the bigger bullet slows the velocities down enough for the bullet to hold together better. I take it you don't roll your own ammo so what you need to do is search for good hard bullets. Anything with a monolithic bullet would serve well more than likely. Those fusions are SUPPOSED to hold together well at short range impact velocities but I haven't personally tested them so I can't speak to the honesty of that. Barnes has a cartridge loaded with their TSX bullet that does hold together exceptionally well. If your rifle will shoot it accurately, that would be the first round I would try.
https://www.midwayusa.com/product/15...free-box-of-20 there's you a link for it. 160 grain is a pretty good weight for the 7mmRM.