Once again writers read into things what they want to.
Nowhere in his writings does Jim Corbett refer to his .275 Rigby. He only refers to a .275 rifle. Although he was supposedly presented with a Rigby .275 rifle he never refers to this presentation or the rifle, only to the .275 Westley Richards he himself purchased from Manton's and with which he missed a perfect close range opportunity to take out a man-eater when he failed to take up the second stage on the Westley Richards 2 stage trigger, thinking he had failed to chamber a round. This all happened TWO YEARS after he was supposedly presented with the Rigby .275 rifle. Unless the Rigby had a single stage trigger surely if Jim had used his Rigby he would have been familiar with a 2 stage trigger, not unfamiliar as he admitted. Jim did not refer to a 275 Rigby.

Likewise Bell refers to the 7x57 or .275 rifle.
Search online and images of early ammunition refer to .275 FOR Rigby rifles, that is different than .275 headstamped cartridges. It is only the later custom ammo such as Hornady that have headstamped cartridges .275 Rigby.

Writers need to read the books written by the original authors before continuing to perpetrate fallacies.