What kinda 45-70 you got?? The Lyman book (and others) list two different sets of loads. One or the 1886Winchester and the 1895 Marlin, and another set for the Ruger #1.
For the 1886, the Lyman shows a start of 36.0 and a max of 38.0. For the Ruger #1 & #3, it shows a start of 38.0grs and a max of 45.0grs.
To work up a load you might want to begin loading 3 cartridges at a moderate charge. Put them and a scrap of paper with the load data on it in a baggie. Then load 3 more at a grain or 1/2 grain higher and put them and the data in a baggie. And so on until you get to around 80-85% of max. Shoot these and see how they look and how the load feels and which one is more accurate. Go from there, easing more toward max is possible. Once you get your best load with this technique, you can start fine tuning it with =/- one of two 10ths of a grain.