extruder screw and barrel steel bullet is pressed in

Gunpowder is packed into this, and then a lead or extruder screw and barrel steel bullet is pressed in. The percussion cap contains fulminate of mercury or some other substance that explodes from shock.The spark would fire the gunpowder and make it explode. Big cannons were soon using the same kind of ammunition as the pistol or rifle, but the "bullet" is called a shell and the explosives are contained in a shellcase. The cartridge has a hollow shell made of brass. At the closed end of the brass shell is a percussion cap ("percussion'' means "striking"). The shells barrel and screw used in artillery are so big that each contains a big charge of explosive that explodes when it strikes the target, causing much more damage than plain metal could. Pulling the trigger of the gun makes the hammer strike the percussion cap. Next came the cartridge, as it is known today.
. Cannons were fired in much the same way. It explodes, which makes the gunpowder explode, and off flies the bullet.

Shells used in shotguns are made the same way except that many small lead balls, called shot, are packed into a cardboard case with a charge of gunpowder and a percussion cap at the end