The 45 70 will kill anything quite handily with the standard 405 gr loads at 13 or 1400 fps. There is really no need to take this cartridge to the max in my opinion . The problem is people try to make the 45 70 into a 270 . It isn't a long range cartridge and never will be.You are punishing yourself for nothing, use it within it's effective range of around 100/ 150yds .Think of it as a bp rifle which is what it originally was, 45cal /70 gr of bp.
If you want to shoot fast bullets a long ways then get a modern 30 cal rifle designed to do that. easy peasy just my opinion though ,if you really like the shoulder bruises... carry on
