I did a little research on line. Apparently, the 45-75 sharps was the civilian version of the 45-70 Gov. cartridge. The 45-75 Winchester is a bottle necked cartidge with a fatter case than that of the 45-70. So, If your wanting to shoot the 45-70 in a 45-75 Sharps. Then, according to what I read. It would be perfectly safe. I did some checking. The 444 Marlin is faster than the 45-70. I'll have to find my other manuals. this maual doesn't give energy levels for any loads. It just gives bullet density. It gives four loads for the 180 grain bullet. And four for the 240 grain bullet. The fastest is 2500 fps for the 180 grain bullet,and 2300 fps for the 240 grain bullet. The only weight bullet it shows for the 45-70 is the 300 grain bullet. I'll have to get serious and get my other manuals out. I have an idea where to find them. I'll check some more and let you know what I find once I find my manuals.
Did you know that there were 6 different rifles that were built for the 45-70? And, that they all have different pressure levels that they can handle? Interesting,Huh? It shows 4 loads for the MDl 1873 Springfield, Remington Rolling Block, And other old blackpowder replica rifles. Six loads for the MdL 1886 Winchester. And, five for the Mdl 1895 Marlin,and Ruger No.1 and 3 rifles. The marlin and Ruger loads are the hottest and fastest. the Remington, and Springfield are the slowest.