RE: 45-70 bullet choices
Expansion trouble could be solved by shooting the same bullets at a higher velocity, or using a softer bullet. IMO, it would be a mistake to use a lighter than 300-grain bullet in the .45/70! The 300 is actually a little on the light side for that caliber.
I use 400-grain Speer flatnoses and Barnes Originals. If you loaded the 400-grain Speer flatnose or even the Remington commercial 405 grainer up to 1800 FPS, it will more than make a big hole in things! 53 grains of IMR 3031 with either of these bullets is plenty, even for Grizzly bears!
The .45 caliber rifle bullet is one which is sufficiently large, it does not need to expand at all to make a large wound channel through game animals.