A shotgun shell (shotshell) is a self-containe cartridge loaded with shot or a slug designed to be fired from a shotgun. Most shotgun shells are designed to be fired from a smoothbore barrel, but with the recent gain in popularity of dedicated shotguns with rifled barrels for firing slugs, there are many rounds specifically designed to be fired from a rifled barrel. A rifled barrel will increase the accuracy of the shotgun with slugs, but makes it unsuitable for firing shot, as the rifling causes the shot to form a hollow "O" shape in flight.