The term is often applied to illegal weapons that are created by cutting off the barrel of a standard shotgun. The barrel of a shotgun without a tube magazine can be cut to any length; pump-action or semi-automatic shotguns usually have a tube magazine attached to the underside of the barrel which limits the practical minimum barrel length to about the length of the magazine tube, unless it also is modified, technically much more challenging than shortening the barrel. Repeating-fire shotguns with box magazines do not lose shell capacity when sawed off, but they are far less common than those with tubular magazines. Shotguns manufactured with barrels under the legal minimum length frequently fall into special categories.