45-70 is an awesome caliber. My 90 lb daughter shoots it with no problem. 400 grain lead bullet 12.0 grains of unique. Bullet is just under the speed of sound. Very pleasnet to shoot.
That load comes from a very old Lyman book and you can google GMDR lever action for some other nice pleasant loads.
I use the 400 grain lead bullet alot. It is a good fit between the teeny bullets of 250-350 grains and the heacy weights 500-600 grains. I shoot alot of casts, I have a nice little 250 grain bullet mold that is fun to shoot also,
For big boy loads in the 45-70, Reloader 7, IMR3031, H322 or IMR 4198 are good choices.
Pops always said if you want velocity and reasonable accuaracy Rl7 or IMR 3031. If you want accuracy and reasonable veloctiy IMR4198. YMMV