I consulted Jon Speed directly.

Jon,

I’m having a friendly argument with Dorleac on NE concerning whether Rigby ever used slant box actions to build .350 Magnum caliber rifles. I advance the opinion that all stepped ring magnum length actions had slant magazines, which he disputes.

There is a rifle currently up for auction on Proxibid which is ostensibly caliber .350 Magnum and so marked on the receiver ring, but appears to me to have a slant magazine. https://www.proxibid.com/Oberndorf-Rigby-Mauser-Bolt-Action-Sporting-Rifle/lotInformation/47410040
Can you settle this disagreement?

Thanks,
Bill

This was his reply:

"Bill. I agree that all Rigby magnum 400/350 magnums had step down rings and slant box magazines. However, its possible that when assembling the later Rimless .350 magnum they may have used up an inventory slant box unit that can be made to handle the rimless .350 etc. So No this was not Original to the Normal Ring .350 Rimless magnum rifle. Dumb events like this occur every so often and confuse folks. Regards, Jon"