Another possibility would be the little-known-but-long-remembered 35-50 Maynard, a very late development in Maynard's history just prior to their bankruptcy. Parent case is generally conceded to be the 30-40 but little reliable original data is extant. James Grant treats of this subject in 4 of his 5 books and still didn't arrive at any firm conclusions.

However the NRA has legitimized at least one version of this cartridge for use in the BPCRS game and therefore reamers, dies and loading data already exist for it. For details you can contact Dangerous Dan the Torpedo Man (Dan Theodore), he was the driving force behind the NRA's decision and he'll know where to find the gear for it.
Regards, Joe

You can lead a man to logic but you can't make him think. NRA Life since 1976. God bless America!