While perusing the interwebs, I came across a Ruger No.1 chambered in the 416/470 cartridge. That is, a 470NE necked down to 416.
Thinking this must be a fairly recent development, I looked into it further and came up with this:

https://www.africahunting.com/threads/416-470-sxs-double-rifle-john-rigby-co.2743/

So, I guess Rigby had done this well before the 500/416 which is similar but 1/4" shorter and of course the new 416 No.2 which, in length, is somewhere in between and dimensionally the same as the rimless 416 Rigby.

Which brings us to this:
http://www.cartridgecollector.net/416-flanged-magnum

And this:
https://www.gunbroker.com/item/807208602

So, maybe 'ol Butch Searcy beat Rigby and Dr. Stief to the 416 No.2 quite a few years ago!