4seventy:
Jack's much-publicised late shot on that buffalo has probably over-shadowed the true problems, one of which was that the original powder charge was compressed, and would expand over a year or two in storage as the powder began to break down in Africa's tropical climate. This pushed the bullets out to varying degrees. Game Departments that had laid-in a large stock of ammo for elephant control were experiencing feeding problems due to the over-length cartridges hanging-up in the mag box, and erratic ignition from the degraded powder. This has been reliably reported a number of times, but the exact references escape me at the moment.

Modern 2150 fps loads with single-base powders, especially the ADI range (=Hodgdon 'Extreme'), do not need to be compressed, and don't break down in decades.

The .458 Win Mag handloaded today is indeed the cartridge the original designers had hoped for all those years ago.