A bullet is a small, heavy, pointed object that is fired from a gun at high speed. Bullets are made mostly from lead coated in copper. The reason they are coated is because lead has a relatively low melting point, and in some guns the bullets come out of the gun so hot the lead melts. Copper has a higher melting point. Bullets existed before guns, and were much rounder and made of lead or were just small round stones. They were used in slingshots.