First of all I am not sure that my answer is correct. There were many "elephant" guns before 1911, but in that year John Rigby invented the 0.416 cartridge which was a big improvement on previous ones for big game.
Therefore the 0.416 Rigby Rifle was developed in 1911 for the ivory trade.
Thank you for your thoughts. I've spent ages researching the clue. The category heading is "Not what it seems" and all the other answers are words that fit that so not sure what to put for this one.