I haven't found a caliber breakdown for the High Wall, but .45-70 was the mililtary caliber during its heyday so I would think it reasonably common. There is a tendency to think of those as was said about Webleys, "They never made two alike." Not true of either Winchester single shots or Webleys, but there are so many variations and extras for those guns that there seems to be no "standard" caliber or configuration. I suspect most were special ordered rather than "off the rack" purchases.
Great gun, though. I think we would like to see pictures.
Jim