I don't know if a .45-70 would hold 90 Grains of black powder? Well, probably FFF would do it, but usually the heavier the bullet , the lighter the charge because of pressure and recoil. But the .45-70 was one of many big bore cartridges built on a "basic" case. They cut it off, made the mouth wider, necked it down and did all kinds of altrations the basic case. But in the black powder era they couldn't get much velocity so they had to depend on bullet weight for killing power. The biggest one I recall in common use was the .50-90 and I am sure there was bigger when the first Safaris were being set out in Africa, but I am speaking of U.S cartridges. I think Sharps was the company that originated the first big bores for buff, but not positive.