It is very hard to say on the 45-70 and it varies for alot of reasons. I load 60 grains of 2f, an eighth inch grease cookie wad and a 500 grain, (Ideal No.457125 mold) PURE lead bullet, lubed with that red wax that surrounds Gouda cheese 50-50 with bees wax. (Laugh all you want) Then I load it in a 45-90 ideal tong tool. The loaded shells then are long enough to press the bullet nose into the rifling when I close the 1884 Trapdoor breech block.
In addition the pure lead can be "upset" or swaged into the rifling on ignition. Now I don't use a drop tube, but I use a plunger type brass valve that screws onto the powder can. The outlet of the valve slip fits into the 45-70 shell and I hold it upside down and shake it back and forth three or four times, close the valve and lift the can and vallve from the case. It turns out to be just perfect with the grease cookie wad, to compact the powder about one sixteenth of an inch when fully seating the big 500 grain bullet.
Powder to a sixteenth of the case mouth sounds like too much. When you press the bullet into the case with force to compact it, the case could "bell" and not chamber.