When I was developing loads for my 458 American in the SMLE, basically the same case capacity as a 45-70, I contacted AA for information on which powder(s) of theirs would work the best at <45KCUP. Johan replied that AA2460 was 5% lower in pressure at equal amounts so I tried it.
AA2460 gave me the highest velocity and lowest pressures and longest case life of ANY powder I had tried so far...ALL the powders except VV that fell into that specific pressure range for the specific case volume of those cases.
The most accurate load, ~<1" at 125yds with the Lazer cast, 430 TrueShot "Silver bullet" would give me well over 10 firings per case...10 being my limit for heavy loaded rounds. AA2230 would be giving up at 8-10 firings and some of the other faster burining powders like 4198 only give 5 or so...H4895 was also a good one.
Varget was a bit slow for my taste, but gave a full case, good accuracy but lower velocities than I wanted. RL-15 was also good for a full case, low velo but accurate with several bullets from 300 to 525 gr.
I like a full case right to the base of the bullet and slightly compressed, which also helps keep the bullet from moving backwards from recoil and getting whacked by the other bullets in the tube mag...bullet movement is not quite as bad in a stack mag if you have a tight neck fit and crimp.
Lots of good powders and bullets for the 45-70 for whatever weight and velocity you happen to like. I shoot more bullets over the chrono than in the field definitely when it comes to all my large cals...but those large cal, heavy bullets whack, dig a hole and bury all those sageratz that happen to get in the way...Hahahahahah
Luck
