Quote: The Mausers that Rigby’s 400/350 was built upon was an entirely new action from Mauser, not a modified standard action. All Rigby did was tell Mauser what they wanted and Mauser made it.
Which reinforces my point that Rigby could have simply used a rimless version of the 400-350, but they didn't.
It would have been far easier to get Kynoch to supply a rimless version than to get Mauser to build a completely new action!