Well, folks, record has it that two mature bull elephant have been taken by the same person with a .22LR rifle.
The noted late Bwana Peter Hathaway Capstick recounts this tale in one of his well-written Africana tomes, "Death in the long grass", I believe. I also read it in one of the previous editions of Charles Barnes' "Cartridges of the world". Here's how it happened.
One day, a white farmer living in a southeastern African country woke up to see a large bull elephant gingerly devouring his precious crop. After trying to shoo off the beast in vain, he decided to resort to his .22LR rifle. By giving the pachiderm a good sting in the backside - he thought - the animal would move off and leave the crop alone.
After firing the shot, he saw instead - with dismay - the beast instead piling up, quite dead. Upon examination of the carcass, he found that he had struck the elephant in the back of the knee, hitting an artery and subsequently killing the animal from blood-loss.
This became quite a story in the farmer's town, until it reached the ears of a white hunter. He could not believe the story, and challenged the farmer to repeat the feat for a wager - which he actually did several days later.
I personally believe the story. Hey, if anything can be killed with a needle, the same applies for a good .22LR!!!