How big are the steel balls for slingshots?

A steel ball with a diameter of 9 mm. The slingshot of 9 mm diameter steel ball has a range of more than 50 meters, and can even hit more than 80 meters, which is very powerful, so the slingshot of 9 mm diameter steel ball has the greatest lethality. Slingshot is a cold weapon or a game tool. A slingshot consists of a bow, a rubber band and a leather bag. It is a "ya" shape made of branches. Rubber bands are tied at both ends of the rubber band, and a piece of skin wrapped in a projectile is tied in the middle of the rubber band.