I'm not aware of any formula for it.
My guess is that when nitro powders developed, makers proved (or attempted to prove)existing actions and built up from there to where the actions could pass proof.
Steel technology saw improvements during the same time period too.
Also, you will notice that a double rifle action bar is generally not much narrower than the balls/fences of the action whereas a shotgun action has a much narrower bar. That's why rifles built on shotgun actions often look a little wonky compared to benchmade nitro rifles.
I know of a Purdey hammer double that actually cracked in the corner and I think we all witnessed an Alex Henry not long ago with the same sort of failure. Surely from shooting full nitro loads in these BPE rifles.