The cartridge in question would be the 338/375 Chatfield Taylor. It was originally made by necking 338 Win Mag cases up to 375 but can also be made by necking down 458 Win Mag brass.
A mate had one done on a stainless Ruger about 10 years ago and it could produce 375 H&H velocities no problem, and with a lot less recoil but at a higher chamber pressure.
The main idea was to equal H&H velocities in a 30-06 length action.