Burn rate charts can be very misleading. First off RL22 is far denser than IMR7828 or H1000. You can use these powders to achieve similar results but you first need to understand that powder weights won't be identical and maybe not even close.
Both of the suggested equivalent powders have very similar or slower burn rates but are much bulkier.
I see from your post that you are for some reason limited to Hodgdon's offerings. That isn't a bad thing but can be limiting.
I agree with Ganderite, H1000 would be a better choice than H4831 which is much quicker and maybe even to quick for the cartridge you describe.
I believe there are factory loads available and RL 25 is the powder used in them.
This is a long range cartridge. Used for distances up to and beyond 2000 meters.
An acquaintance of mine has one. He uses Retumbo, H1000 and 50BMG. This thing has a voracious appetite for powder. I guess if you have to ask, you really can't afford it.
From what I remember, Retumbo was OK with lighter weight bullets but H1000 was much better velocity and accuracy wise with heavier bullets. 50BMG worked well but wasn't his powder of choice.
Like you he found very little information available and had to carefully work up a load for his rifle. I don't know what his loads were but I do remember the cost was way up there to shoot regularly. I try very hard to stay away from this sort of round. Fine if you can handle it.
