Don't look at Unique powder in 4oo-550 grain gas check bullets as being "weak plinkers," in the 45-70.
I have a copy of the original edition Lyman book of cast bullets and I am looking at a load of 20 grains of Unique with a 500 grain gas check bullet. They give the velocity as 1625 fps, which is a right smart load for the 45-70 and well above the traditional safe load for old Springfield Trap Door rifles. Also, well above any factory sporting load, which are held at about 1450 fps, considered safe for the Trap Door.
The 45-70, using Springfield Trap Door rifles was the official US Army rifle for two years, prior to the introduction of the 1903 Springfield bolt action magazine rifle.
Wife and I once spent several days with a metal detector on an old US Army Fort on the Colorado River in Arizona. We found a history lesson full of empty 45-70 cases, all of which had been loaded with the earliest versions of smokeless powder and using the original methods of primers firing them, including the first center fire primers, which was a primer pushed in the case and fired by a center fire hit. The case looked just like a rim fire, only fired by a hit in the center of the base.
Empty cases with date stamps used for smokeless powder, started at 1882.