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Polygonal rifling is a type of gun barrel rifling where the traditional lands and grooves are replaced by "hills and valleys" in a rounded polygonal pattern, usually taking the form of a hexagon or octagon. Polygons with a larger number of edges provide a better gas seal in relatively large diameter polygonally rifled bores. In the Glock pistol, for instance, octagonal rifling is used in the large diameter .45 ACP bore, which has an 11.23 mm (0.442 in) diameter, since it resembles a circle more closely than the hexagonal rifling used in smaller diameter bores.〔(Barrel History )〕 ==History== While polygonal rifling has been around since the earliest days of rifled barrels, it had faded out of use by the time of the early cordite cartridges. The principle of the polygonal barrel was proposed in 1853 by Sir Joseph Whitworth, a prominent British engineer and entrepreneur. Whitworth experimented with cannons using twisted hexagonal barrels instead of traditional round rifled barrels, which was patented in 1854. In 1856, this concept was demonstrated in a series of experiments using brass howitzers. The British military, however, rejected Whitworth's polygonal rifled designs. Whitworth believed that polygonal rifling could be used to create a more accurate rifled musket to replace the Pattern 1853 Enfield. During the American Civil War, Whitworth's polygonal rifled Whitworth rifle was successfully used by the Confederate States Army Whitworth Sharpshooters. The Whitworth rifle is often called the 'sharpshooter' because of its accuracy compared to other rifled muskets of its era (comparable to the Sharps Rifle?), and is considered one of the earliest examples of a sniper rifle. The last common rifles to use polygonal rifling were the Lee–Metford rifle, named after the Metford rifling, and the Arisaka rifles designed by Col. Arisaka. The switch to cordite from black powder proved too much for the shallow rifling in the relatively soft barrels of the Metford, and the Lee–Metford became the Lee–Enfield when the Metford rifling was dropped. However, Arisakas were manufactured until the surrender of the Imperial Japanese Army in 1945; it has been proven that Arisaka rifling was more durable, and the accuracy of many captured rifles can attest to this. During World War 2, polygonal rifling emerged again in the German MG 42 machine gun. It was an outgrowth of a cold-hammer forging process developed by German engineers prior to World War 2. The process addressed the need to produce more durable machine gun barrels in less time than those produced with traditional methods.〔(Barrels and Bullets: Conventional Versus Polygonal Rifling by Dennis Cantrell 06/08/2010 )〕 The MG42 successor, the Rheinmetall MG 3 machine gun, can also have polygonal rifling. Heckler & Koch was the first manufacturer to begin using polygonal rifling in modern small arms like the G3A3 assault rifle and several semi automatic hunting rifles like the HK SL7.〔(SL7 Polygonlauf, Vielflächenlauf by Lutz Möller (German) )〕 Companies that utilize this method today include Tanfoglio, Heckler & Koch, Glock, Magnum Research, Česká Zbrojovka and Kahr Arms. Polygonal rifling is usually found only in pistol barrels, and is less common in rifles; however, some extremely high end rifles like the Heckler & Koch PSG1, Precision Sniper Rifle PSR 90, and the LaRue Tactical Stealth System sniper rifle use polygonal bores. The term "polygonal rifling" is fairly general, and different manufacturers employ varying polygonal rifling profiles. H&K, CZ and Glock use a female type of polygonal rifling similar to the bore shown above right. This type has a smaller bore area than the male type of polygonal rifling designed and used by Lothar Walther. Other companies such as Noveske (Pac Nor) and LWRC use a rifling more like the conventional rifling, with both of each land's sides being sloped but having a flat top and defined corners; this type of rifling is more a canted land type of rifling than polygonal rifling. 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「Polygonal rifling」の詳細全文を読む スポンサード リンク
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