Daryl,
I was going back over some of these posts and found yours about pressure and velocity of some 45/70 rifle loads. Some time back I built a .405 Winchester for a friend and we regulated it with a 300 grain jacketed spire point bullet at 2100 FPS using Varget powder. Not a really hot loading, but crisp. I had initially thought that I wasn't going to like this caliber in a double rifle, but that gun changed my mind very quickly because it seemed that it was out performing any 45/70 loading that I had come up with to date. I realized two things, because it was somewhat smaller in frontal area, and because it was using spire point bullets, it was holding up it's speed much better.
Then I realized that because we can shoot a spire point bullet in our double 45/70's, plus the fact that spire point bullets are now available in the .458 size, there is no reason that the 45/70 couldn't be boosted up to .405 speed in a 45/70, as long as the action is strong enough to take it.
What powder would you recommend using in a good strong 45/70 double to get 325 grain bullets up to 2200 FPS safely? Would varget do it? I have also just bought some Hornady 300 grain Interlock bullets in .411 for the .405 Winchester and some 325 grain Hornady FTX .458 bullets to try in my 45/70's. Any load over 2000 would be fine by me for the 45/70 325 grain loads. I just wonder also if these FTX bullets will reliably open up at 2000 FPS? Bob