How the Rifle and Handgun Fires A cartridge is inserted into the chamber. The action is closed, and the firing pin is pushed back and held back under spring tension. The trigger is squeezed, releasing the firing pin, which moves forward with great force. The firing pin strikes the primer, causing it to explode. The spark from the primer ignites the gunpowder. Gas converted from the burning powder rapidly expands in the cartridge. The expanding gas forces the bullet out of the cartridge and down the barrel with great speed. The rifling in the barrel causes the bullet to spin as it travels out of the barrel. The bullet's speed and escaping gases produce a "bang."