The Brit who died from a lion mauling on the Athi Plains was George Grey, brother of Edward Grey who later became British Foreign Secretary.
He was new to the game of riding lion but dismounted to receive the lion charge in traditional style. Unfortunately his 2 shots from the .280 Ross Sporter failed to achieve satisfactory conclusions!

He was hunting with Sir Alfred Pease at the time, author of "The Book of the Lion", who wrote about the incident in his personal diary. Capstick included the account verbatim in an Editor's Note in the preface to his Reprint Edition by the same name.

and...

As I'm sure you know mckinney, original Type A Mausers chambered for the .280 Ross were magnum length.
They do turn up occasionally, but you will need deep pockets!