I never loaded for the 45/70 but my bullet and load selection would depend on what I intended to use the rifle for. If hunting large body animals then I would try a good charge of IMR 4064 (51-54 gr) and see how they shoot. My old Speer manual's #1 powder for a 400 gr bullet is H335 which requires a LRM primer. If you want a light load then SR 4759 is good for reduced loads. Whatever you use the Henry will be a thumper. When I load I look for accuracy first and ft/lbs secondary. I figure a less powerful shot in the right spot trumps a big blast in the wrong spot.