I came across two unopened cans of Hercules Reloader 21 (I'll refer to it as H21) yesterday. I am using the same square can vintage of H2400 in the 45/70 with much success and expect this to be good powder once I unseal one.
I would like to use this powder for is to push cast boolits, and maybe a few jacketed rounds out of the 35 Whelen for trial and fun. The research so far has shown that H21 is one number slower than Reloader 22. Some say drop a grain or two to extrapolate, others have mentioned use RL15 data, as it is faster than H21 and increase as necessary. Though there is published load data that I can find for the 30/06, I don't have load data for the 35 Whelen that I have found, yet. I used to have a Speer Manual #8 but haven't seen that since a move 10 years ago to consult.
I do have an ancient Speer Manual #5 that my Grandpa used that has load data for the old Hercules Hi-Vel powder in the 35 Whelen, that is said to have been replaced by H21. Some sources say to use that data interchangeably. I would like to be directed to established sources before proceeding, though. Anything you fine gentlemen can pass on is greatly appreciated.
Ignore the thumbnails for H12. That was another subject but they did not delete due to my ignorance.