The firearm design is the critical factor in determining the load parameters in a .45/70. For example, the old Trapdoor Springfield action (including modern made examples) is notoriously weak and must only be used with loads that equate to the original black powder service load. Rolling blocks and M1886 Winchesters are better. Modern single shots and new production Marlin lever actions are better again and are suitable for any modern factory load. In a strong front-locking bolt action then the .45/70 can be loaded to .458 Win Mag levels in modern solid head cases Such rifles are custom made. I made one many years ago for a customer based on a Winchester P14 action that was commonly loaded to .458 levels and flattened animals at 2-300 metres, but the big round nose projectiles stated to drop noticeably after that range, even after starting out at over 2500 fps.
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