Never bring a stone to an Elephant fight

[Frostbit]

"An elephant turned violent on Tuesday and trampled a man to death in Mashonaland Central's Mvurwi district after locals pelted the animal with stones, the Zimbabwe Parks and Wildlife Management Authority (ZimParks) has said."

LINK

Personally I don't recommend a stone smaller than 400 grains moving at 2150 FPS or greater.