A semi-automatic firearm, also called a self-loading or autoloading firearm (though fully automatic and selective fire firearms are also self-loading), is a repeating firearm whose action mechanism "automatically" loads a following round of cartridge into the chamber (self-loading) and prepares it for subsequent firing, but requires the shooter to "manually" actuate the trigger in order to discharge each shot. Typically, this involves the weapon's action utilizing the excess energy released during the preceding shot (in the form of recoil or high-pressure gas expanding within the bore) to unlock and move the bolt, extracting and ejecting the spent cartridge case from the chamber, re-cocking the firing mechanism, and loading a new cartridge into the firing chamber, all without input from the user. To fire again, however, the user must actively release the trigger, allow it to "reset", before pulling the trigger again to fire off the next round. As a result, each trigger-pull only discharges a single round from a semi-automatic weapon, as opposed to a fully automatic weapon, which will shoot continuously as long as the ammunition is replete and the trigger is kept depressed.