Jim,
The British Gun Makers had, of necessity, to design and manufacture their own ammo for Big Game as there was nothing else available anywhere. The largest the Americans had was the 50-90, which whilst it may kill a Bison was not a calibre anyone with any sense would use against Rhino or elephant or any of the dangerous African and Indian big game. The breech loading 2,4 or even 8 Bores had wicked recoil when fully loaded and that's why gunmakers went for rounds that were more manageable but would still knock down and kill a dangerous animal. With the advent of Nitro powders i.e. Cordite, enabled many of the old BP rounds to be upgraded and to use heavy jacketed bullets. The reason that British ammo for these large calibres is expensive is that the demand is no longer there to permit volume sales, Big Game hunting as far as we Brits were concerned had it's death knell in the 1930's it got too expensive. It also became and more and more and expensive A Safari today can set you back many tens of thousands of Dollars to the hire of a professional hunter and his staff, then there's travel costs in country, game licences which alone can run to several thousands of Dollars, have pushed this sport to beyond the reach of even a fairly wealthy man.
Most Big Game hunting today is done with a camera. That's affordable.
Several thousands of Americans may have bought 458's, but I'd bet less than a quarter of one percent of them have taken theirs to another country where is suitable for hunting. I'd also bet most never got anywhere other than a rifle range. Any American would be vastly over gunned, if they are using it in the USA for hunting.
Harry.
