far less expensive since they do not require the precise aligning of parallel barrels. Single-barrel shotguns are also lighter, which can be an advantage if they are carried hunting, though it does mean they have more felt recoil. They are not widely used in shotgun sports, as most events require the ability to quickly fire two successive shots. The single-barrel shotgun is often referred to as a "kitchen door gun" or a "farm gun" due to its low cost as a self-defense weapon. Types of single-shot cartridge actions Trapdoor actions The earliest metallic-cartridge breechloaders designed for general military issue began as conversions of muzzle-loading rifle muskets. The upper rear portion of the barrel was filed or milled away and replaced by a hinged breechblock which opened upward to permit loading. An internal angled firing pin allowed the re-use of the rifle's existing side-hammer. The Allin action made by Springfield Arsenal in the US hinged forward; the Snider–Enfield used by the British opened to the side. Whereas the British quickly replaced the Snider with a dropping-block Peabody-style Martini action, the US Army felt the trapdoor action to be adequate and followed its muzzleloader conversions with the new-production Springfield Model 1873, which was the principal longarm of the Indian Wars and was still in service with some units in the Spanish–American War. Other trapdoor actions include the rare Confederate Tarpley carbine, the Austrian Wanzl, the Belgian Albini-Braendlin rifle and Terssen conversion (some of which were made from French 1777 pattern flintlocks), the M1842/59/67 Swiss Milbank-Amsler, the M1859/67 Spanish Berdan, and the Colt-manufactured Russian Berdan Type I. All of these designs save the 1863 Tarpley date from the period 1865–1869, and all but the Tarpley and the Russian Berdan were conversions from muzzle-loaders. Break actions Perhaps the most common type of single-shot action, usually found in shotguns, small pistols, and black-powder "elephant" guns, a break action connects the barrel assembly to the breechblock with a hinge. When a locking latch is released, the barrel assembly pivots away from the receiver, opening the breech and sometimes on higher quality firearms, partially extracting the spent cartridge. Rolling block actions In a rolling block action, the breechblock takes the form of a part-cylinder, with a pivot pin through its axis. The operator rotates or "rolls" the block to open and close the breech; it is a simple, rugged and reliable design. Rolling blocks are most often