I know that the 458X2" American was designed by Frank Barnes as an all all around North American big game cartridge for places like Alaska.
I first saw it in cartridges of the World, so you can likely find data there, and for sure the Barnes manual.
I danged near bought one a few years back for an old fella in Edmonton(I think) ,it was in the firearms trader , but by the time I decided to, it ws gone!
Wonder if it was the same one?
Cat