reneerick,
Coyote Hunter and Bestboss are arriving at the same place with two differing methods. . .C-Hntr with a variety of slugs and powders. . B-boss with differing powders/ and/or charges. ( Mind you, reneerick, there are some powders that can be loaded down to 45 Colt levels all the way up to max level three bruisers).
For the last 30 years I've been in C-Hntr's camp. I've been shooting in five diferent shooting events using over 20 different bullets in 35 different loads, using as many different powders.
I quite last year. It was going to blow up my head with variety-overload. My powder room is better stocked than any store in town. That's NOT RIGHT. So, I'm with Bestboss now. He's answering your question of "one wt" like I would today. Hey, it's a 45-70, designed around the 405gr slug. Learn THAT slug and you can shoot anything on this dirt just shy of Cape & Rhono-class. Pick a powder that can do way up and waaaay down. Then it's only a matter of elevation compensation, not a geologic survey of a new point of impact with a new piece of lead. Some guns can put them ALL inline. Most won't.
I've just completed my 4,500 reloading & shot of a 45-70, in a big variety of loads (six months). I used them all from 300gr's up to 600grs. From the view-point of a burned-out high volume shooter, there is no substitute for knowing a gun well, and shooting that gun often enough to know how it goes bang with THAT bullet.. Ok, variety is the spice of life. But five years ago in a high-power 1K comp I got my butt buried by a geezer gent that shot one load, four distances. Damn that guy knew his gun. Throw in the wind, and this guy humbled a field of national shooters. . . And that was with a bottle-neck.
My point? Damn, I forget. .

. . . but The 400 gr wt is a good place to be. I've got club members that globe-trot & hunt EVERYTHING Mother Earth has to offer, and have been doing so for decades. They Loooove the 45-70. They say that a solid 400-- 500 gr slug, at 1800 fps, will penetrate MUCH further than the same at 22'-2300 fps. (" the faster you go, the faster you stop"). . Plus, you can make that 400 gr feel like a 45 Colt. Pretty cool. My point is that backing down loads works. Just because you can go waaay up, doesn't mean you have to. Want light? Then load light. Dies stay adjusted the same, molds are the same , windage stays the same, inventory stays the same.
I did the math a few months ago. I thought 'light' lead would be cheaper. After the powder, primers, dies, etc were factored in, ONE bullet, one powder, one primer. . it was even. My time is worth a lot, so THAT tipped it to the 405gr. ( not too heavy, not too light). . Bummer that I have over 2000 each of 300, 350 and 500 gr slugs around tho. Sheeese.. .( not to mention the five different powders for the same.) :evil:
Ok, maybe I'm just not in the playing-around mood anymore. I like to spend my time shooting, not tinkering with mega-variety. That's for the younger of you guys, I guess. I have a bunch of primed cases staged and ready. Now it's just powder loads. Simple, ez, fast. Shoot. More time shooting. I've got other calibers to load for.
BTW: I came to this conclusion last night.. . heh heh. That'll teach you to listen to me. Yikes.