Loads for the .45-70. Boy, is that a tough question, sorta like "How high is up?" there just ain't no simple answer.
If you are using an antique gun, or a reproduction of an antique gun, you really ought to use black powder. The gun was designed for lead bullets and black powder velocities, and believe me, it will just plain work better if you use lead bullets and black powder. And remember it isn't just matching the velocity of black powder, you want to match the pressure of black powder. Which is gonna be pretty difficult with smokeless powder. (Some of the black powder substitutes might work well, but I have found them to be more of a problem to work with than real black powder.)
Someone already mentioned "you can't get 70 grains of black powder into a .45-70 case." Well, yeah, you can, you just have to do it differently. If you're using GOEX powder, you will need a drop tube. This is a two or three foot long tube with a funnel on the top. Pouring the powder into a case with this uses the falling of the powder to pack it in uniformly, which you can't do pressing it in with a bullet. But a better idea, if you feel you just have to have a full 70 grains in there, is to purchase some of the Swiss black powder. This stuff is about 15% denser than GOEX, and you won't have any problem getting your full 70 grains in.
I should mention that the best load for any cartridge using black powder, is however much powder you can get in there and still seat your bullet. The exact amount don't mean nothin'.
One of the big problems newcomers to black powder have is with bullet lube. You absolutely can not use any modern, waxy, petroleum-based bullet lube. It just don't go with BP. You need something natural, and the best place to start is with beeswax. I melt it together with the same weight of Crisco, and it works great. Some folks mix beeswax and olive oil. I've tried it, but think Crisco is just as good. This lube is for both your bullets and any sort of wads or cards you might want to use.
Most of the bullet moulds available for the .45-70 are, unfortunately, meant for smokeless powder, and just don't carry enough lube for back powder. You need plenty! Look into the "Big Lube" line of bullet moulds.
And finally, the most important thing about shooting black powder is cleaning up afterwards. This is usually the main reason folks steer away from using The Holy Black Powder. But just one word is the answer to this, and that word is "Ballistol." This wonderous substance is available in both a spray can and as a liquid. You need both, the spray for shooting down the barrel of your guns if you don't want to clean them right away, and the liquid is for mixing with water when you're ready to clean them. You can spray down a black powder fouled gun with Ballistol, and put it back in the safe and forget about it until the next time you want to go shooting. The Ballistol neutralizes the acidity of, and removes the moisture from, the fouling. The mixture on a patch or two will clean out the remaining gunk, and leave a shiny barrel. Dry the barrel, and DO NOT put any petroleum product in there, and you will be ready to shoot the next time.
In case you haven't figgered it out, I have been shootin' black powder for a long time, in muzzleloaders, cartridge guns, single shots, lever actions, shotguns and revolvers.
Grizzle Bear