I have a Henry 45/70 and have been curious about some big thumper bullets myself. Mainly for s**ts and giggles. I found this reference on the marlin owners forum.
http://www.marlinowners.com/forum/45-70 ... 354?page=1"(Forum quote),
I agree with Ridgerunner, something slower like H322 (it is ADI 2219) is more suitable.
I have tried 40grs of AR2219 with 550gr Craters and it seems to be the sweet spot. BUT start at about 36-37grs and then work up and watch for pressure signs. It's ok in my gun but you have to be careful.
I have also tried CBE (Cast Bullet Engineering) 570gr a friend cast (very hard) and I like it with about 38grs AR2219 but again start lower and work up. I really like the heavy weights but remember they are very punishing on both ends. I am bit of a weaky so I use a Past magnum plus recoil shield. I have back problems and no it's not from shooting rediculously heavy loads.
Hope this helps but please show responsibility when going higher in the loads." (End quote)
These guys seem knowledgeable, but of course take this info with cautious mind. Hope it helps.