In my 450 marlin, .5 grain of unique, then a carboard wad, and tamped a round ball all the way inside the case, down on top the wad & powder. These shots are essentially silent, and crono at about 250ft / second. Strangely enough they were quite accurate, and were perfect for grouse. I used them for grouse etc, so as to not spook big game when out hunting.
Don't know if this would work in a 45-70 case. And you absolutely have to check to make sure the barrel is clear before shooting another shot. These silent loads are moving slow, and in theory could get stuck in the barrel. Although I've never had it happen, and have shot a bunch of them.
Fun to experiment with.