https://en.wikipedia.org/wiki/Rubber_bullet
Rubber projectiles have largely been replaced by other materials, as rubber tends to bounce uncontrollably.[9]
Pepperballs sting like hell and have the added feature of powdered OC. They go out at twice the speed of regular paintballs and aerosolize the OC on contact. Mixed rubber ball/pepperball grenades have proved to be incredibly effective in prison riots. Those usually have a flashbang feature as well.
CC