The 50-70, like the 45-70 is a short range cartridge, mainly due to trajectory.
Ballistics tables would lead you to believe it's no where near as effective as modern cartridges. It just aint so.
My experience is with the 45-70, and I have found, that even in it's black powder form, it's killing ability is simply amazing.
Of course like any cartridge, you must select bullets to velocity range, soft lead for black powder etc.
With the 45-70, on moose, I try to keep it to 125 to 150 yards.