There is a massive, unindexed, pile of useful information about reloading the 450b on calguns.net. I will make a small attempt to index the info. Simply search for a powder or bullet or click on the tags.
This is the first about 250 gr Rainier FP with W296 powder:
I started at 10% below the 31.6 gr. of W296 recommendation and worked my way up. The light loads cycled the action but left the casing a little sooty and didn’t flatten the primer, the recommended loads fired cleanly and flatten the primer and even a little hotter load was no where near the kick of the factory loads.
They did require magnum primers too.
This will be a very good starting point, thanks for the help!