Semi-automatic Shotguns are a subclass of shotgun that are able to fire a shell after every trigger pull, without any manually reloading, as is typical in most shotgun designs. The weapon uses the force of exploding gunpowder to both propel the projectile down the barrel, and to cycle the action and load the next round. This process is generally similiar to all semi-automatic weapons, including pistols and rifles. The reason shotguns do not tend to use this system is that shotgun shells are extremely over powered compared to the smaller ammunition used in rifles and pistols, and it is difficult to design parts reliable enough to harness that heavy force for complicated mechanical operations.