often rifle on top, but rifle on bottom was not uncommon). There is also a class of break-action guns called drillings, which contain three barrels, usually two smoothbore barrels of the same gauge and a rifled barrel, though the only common theme is that at least one barrel be smoothbore. The most common arrangement was essentially a side-by-side shotgun with the rifled barrel below and centered. Usually a drilling containing more than one rifled barrel would have both rifled barrels in the same caliber, but examples do exist with different caliber barrels, usually a .22 long rifle and a centerfire cartridge. Although very rare, drillings with three and even four (a vierling) shotgun barrels were made. Pump-action In pump-action shotguns, a linearly sliding fore-end handguard (i.e. pump) is manually moved back-and-forth like a hand pump to work the action, extracting the spent shell and inserting a new round, while cocking the hammer or striker. A pump gun is typically fed from a tubular magazine underneath the barrel, which also serves as a guide rail for the pump. The rounds are fed in one by one through a port in the receiver, where they are lifted by a lever called the elevator and pushed forward into the chamber by the bolt. A pair of latches at the rear of the magazine hold the rounds in place and facilitate feeding of one shell at a time. If it is desired to load the gun fully, a round may be loaded through the ejection port directly into the chamber, or cycled from the magazine, which is then topped off with another round. Well-known examples include the Winchester Model 1897, Remington 870 and Mossberg 500/590. Pump-action shotguns are common hunting, fowling and sporting shotguns. Hunting models generally have a barrel between 600 and 700 mm (24"-28"). Tube-fed models designed for hunting often come with a dowel rod or other stop that is inserted into the magazine and reduces the capacity of the gun to three shells (two in the magazine and one chambered) as is mandated by U.S. federal law when hunting migratory birds. They can also easily be used with an empty magazine as a single-shot weapon, by simply dropping the next round to be fired into the open ejection port after the spent round is ejected. For this reason, pump-actions are commonly used to teach novice shooters under supervision, as the trainer