Bullets are small metal objects fired from guns. Many kinds of bullets are made from lead covered with copper. They are put into a package called a cartridge. The cartridge is put into a gun. The bullet is at the front of the cartridge (number 1 in the picture). The bullet is pushed out of the gun by hot gases at a high pressure. A powder called gunpowder (number 3 in the picture) is put inside the case (number 2). A small explosion from the primer (number 5 in the picture) lights the gunpowder. The gunpowder burns very fast. It makes hot gases. The hot gases are at a high pressure. The high pressure pushes the bullet out of the gun barrel at a high speed. 