I've given that one alot of thought. Pressure wise it would be iffy, 52Kpsi on a 7.62X39 base, but with careful handloading you could get away with it. But the thing I can't get around is the fact that even with the 45/70 you don't have much meat left in the chamber walls, a 50 cal eats that much more. I do know one fella who shoots a 50-70 and I believe that JD is still chambering those, but that's a whole different pressure world.
John A. Monroe, Never Forgive, Never Forget, Blood Pays Blood