Okay, what happened to the British .275 H&H Mag?

Early in the last century it was said to have been the perfect light "plains game" cartridge.

Elmer Keith talks about it in his book, Big Game Rifle & Cartridges. Supposedly it's the forerunner of the 7mm Rem Mag & 7mm Weatherby Mag.

Inquiring minds want to know. Thanks!