Not to in anyway impunge the .45-70, but I seem to recall that Billy Dixon used a .50 cal Sharps on that long range shot at the Indian. I don't recall the exact round, I think a .50-90 perhaps. Wasn't even his own rifle, in fact don't believe he had shot it before. He was considered the best shot by the group so was elected to try. He himself stated it was luck, but obviously he helped "Luck" along with good shooting practises, good range estimation & knowledge of trajectories.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra