All of my .45-70 rifles (and .45-90, .45 Sharps Express, and a few others) were manufactured between 1873 and 1900, well before smokeless powders came into general use. So I tend to treat them gently and load very conservatively. I use cast bullets exclusively in weights from 340 grains to 500 grains. Two powders have proven to be very useful for just about everything, those being IMR-4198 and IMR-3031. Both meter very accurately from my old Lachmiller powder measure.

Even with modest loads the .45-70 is very effective on any North American game. The 500-grain bullet at 1100FPS muzzle velocity will shoot through a 600 lb. elk from end to end. The 340 and 405 grain bullets at 1300-1400FPS put down deer and elk like lightening bolts. There is just no reason to push the upper limits of performance, in my opinion. Enough is enough, and a modest load in the .45-70 is more than enough for just about anything that walks.