Ammunition
They generally store ammunition in detachable box or drum magazines in order to decrease reloading time, whereas most pump-action and semi-automatic shotguns use under-barrel tubular magazines.
Shotguns are able to handle a wide variety of ammunition, however automatics are slightly limited because the shot must provide sufficient force to reliably cycle the action. This means that they are not compatible with low powered rounds, like most less-than-lethal ammunition. The most common ammunition used in combat shotguns is 00 buckshot, which fires about 9 metal balls and is very effective against unarmored targets.
Read more about this topic: Selective-fire Shotguns