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A shotgun shell is a self-contained cartridge typically loaded with multiple metallic "shot", which are small, generally spherical projectiles. Traditionally lead was used, but increasingly steel, tungsten or bismuth shot has replaced lead, due to laws designed to protect the environment. A single, large projectile known as a shotgun slug can also be used, and numerous specialty rounds such as less-lethal rounds (i.e. beanbag rounds), flechette rounds, lead-dust rounds for door-breaching are also available. An old non-lethal shotgun load consisted of a shotgun shell loaded with rock salt, which could inflict very painful, but rarely deadly, wounds, and was therefore popular for scaring away trespassers. Most shotgun shells are designed to be fired from a smoothbore barrel, but dedicated shotguns with rifled barrels may take a number of different rounds. A rifled barrel will increase the accuracy of slugs, but makes it unsuitable for firing shot, as it imparts a spin to the shot cup, causing a centrifugal force that makes the shot cluster disperse.〔http://www.theboxotruth.com/docs/bot43.htm 〕Specialty shotgun ammunition includes non-lethal rounds available in the form of slugs made of low-density material, such as rubber. ==Construction of a typical shotshell== Early shotgun shells used brass cases, not unlike rifle and pistol cartridge cases of the same era. These brass shotgun hulls or cases closely resembled rifle cartridges, in terms of both the head and primer portions of the shotgun shell, as well as in their dimensions. Card wads, made of felt, leather, and cork, as well as paperboard, were all used at various times. Waterglass was commonly used to cement the top overshot wad into these brass shell casings. No roll crimp or fold crimp was used on these early brass cases, although roll crimps were eventually used by some manufacturers to hold the overshot wad in place securely. The primers on these early shotgun shells were identical to pistol primers of the same diameter. Starting in about 1877, paper hulls started to replace brass shotgun shells. Paper hulls remained popular for nearly a century, until the late 1960s. These shotgun shells using paper hulls were nearly always roll crimped, although fold crimping also eventually became popular. The primers on these paper hull shotgun shells also changed from the pistol primers used on the early brass shotgun shells to a primer containing both the priming charge and an anvil, unlike rifle and pistol ammunition, making the shotgun shell primer taller. Card wads, made of felt and cork, as well as paperboard, were all used at various times, gradually giving way to plastic over powder wads, with card wads, and, eventually, to all plastic wads. Starting in the 1960s, plastic cases started to replace paper hulls for shotgun shells. By the 1980s, plastic cases had largely replaced nearly all paper hulls for shotgun shells. Today, modern shotgun shells typically consist of a plastic case, with the base covered in a thin brass covering. As noted previously, paper shells used to be common, and are still made, as are solid brass shells. Some companies have produced what appear to be all-plastic shells, although in these there is a small metal ring cast into the rim of the shell to provide strength. Often the more powerful loads will use "high brass" shells, with the brass extended up further along the sides of the shell, while light loads will use "low brass" shells. The brass does not actually provide a significant amount of strength, but the difference in appearance provides shooters with a way to quickly differentiate between high and low powered ammunition. The base of the shotshell is fairly thick to hold the large shotgun primer, which is longer than primers used for rifle and pistol ammunition. Modern smokeless powders are far more efficient than the original black powder used in shotgun shells, so very little space is actually taken by powder; shotguns use small quantities of double base powders, equivalent to quick-burning pistol powders, with up to 50% nitroglycerin. After the powder comes the wadding or wad. The primary purpose of a wad is to prevent the shot and powder from mixing, and to provide a seal that prevents gas from blowing through the shot rather than propelling it. The wad design may also encompass a shock absorber and a cup that holds the shot together until it is out the barrel. A modern wad consists of three parts, the powder wad, the cushion, and the shot cup, which may be separate pieces or be one part. The powder wad acts as the gas seal (known as obturation), and is placed firmly over the powder; it may be a paper or plastic part. The cushion comes next, and it is designed to compress under pressure, to act as a shock absorber and minimize the deformation of the shot; it also serves to take up as much space as is needed between the powder wad and the shot. Cushions are almost universally made of plastic with crumple zones, although for game shooting in areas grazed by farm stock or wildlife biodegradable fibre wads are often preferred. The shot cup is the last part of the shell, and it serves to hold the shot together as it moves down the barrel. Shot cups have slits on the sides so that they peel open after leaving the barrel, allowing the shot to continue on in flight undisturbed. Shot cups, where used, are also almost universally plastic. The shot fills the shot cup (which must be of the correct length to hold the desired quantity of shot), and the shotgun shell is then crimped, or rolled closed. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Shotgun shell」の詳細全文を読む スポンサード リンク
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