Short Barrel Shotguns have a barrel length of less than 16" and can be shouldered.  You will find many for sale here.  This is a class 3 item-- meaning that you can buy one of these guns in most states, but they must go through a licensed dealer that can deal in NFA firearms.  We can help you with this process.  An AOW shotgun is one that is not shouldered, but just held in the hand.