"Colts New Apex" SIX CALIBRE Revolver:

This conceptual revolver is another variation that would fire its cartridges from the bottom chamber.  

 - Here's a poster for a collectable (fictional) multi-calibre revolver:

" The "New Apex" may puzzle some readers. The upper cylinder contains six chambers, one for each of the various cartridges. The lower cylinder contains six barrel bores, of six different calibres, - one to match each chamber.
 - The mechanism required to make the cylinders rotate in unison is very simple. - No thought whatever has been given to it.
  No further information will be released on any of these Fancy Free revolvers until after the return of the first space ship to visit Mars. "

Chapter 12 'Fancy Free' of Firearms Curiosa by Lewis Winant features drawings of unreal guns by a Stephen Ickes.

I remember reading somewhere that if you can imagine something - it may well be created! - Such a multi-calibre firearm as this would be usefully versatile. - Well, the double-barrelled pump-action shotgun has materialised (DP12 MSRP) - so why not?

 - Life is good.

Marty K.