What element does a semi-automatic pistol use to function?

A semi-automatic pistol functions by using the energy generated from the fired cartridge. When the trigger is pulled and the cartridge is fired, the expanding gases from the ignited gunpowder propel the bullet forward and simultaneously work to cycle the action of the pistol. This energy operates the mechanism that ejects the spent shell casing, reloads a new cartridge from the magazine, and resets the firing mechanism for the next shot, all without any additional effort needed from the user.

This self-loading feature distinguishes semi-automatic pistols from manual action firearms, where the user must exert muscle power to cycle the action, or from fully automatic firearms that continuously fire as long as the trigger is depressed. The option regarding an external power source is not applicable as semi-automatic pistols are designed to operate purely on the energy from the fired cartridge. Mechanical lever action, on the other hand, is characteristic of different types of firearms and does not apply to the operation of semi-automatic pistols.