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Choke (firearms)
In firearms, a choke is a tapered constriction of a shotgun barrel's bore at the muzzle end. Chokes are almost always used with modern hunting and target shotguns, to improve performance. Their purpose is to shape the spread of the shot in order to gain better range and accuracy.〔Shotgun. (2011). Encyclopædia Britannica. Retrieved February 5, 2011, from Encyclopædia Britannica Online Library Edition: http://www.library.eb.com/eb/article-9067520〕 Chokes are variously implemented as either screw-in replaceable chokes, selectable for particular applications, or as fixed, non-replaceable chokes, integral to the shotgun barrel. William Wellington Greener is widely credited as being the inventor of the first practical choke, as documented in his classic 1888 publication, ''The Gun and its Development''.
Chokes may be formed at the time of manufacture either as part of the barrel, by squeezing the end of the bore down over a mandrel, or by threading the barrel and screwing in an interchangeable choke tube. Chokes may also be formed even after a barrel is manufactured by increasing the diameter of the bore inside a barrel, creating what is called a "jug choke", or by installing screw-in chokes within a barrel. However implemented, a choke typically consists of a conical section that smoothly tapers from the bore diameter down to the choke diameter, followed by a cylindrical section of the choke diameter. Briley Manufacturing, one maker of interchangeable shotgun chokes, uses a conical portion about 3 times the bore diameter in length, so that the shot is gradually squeezed down with minimal deformation. The cylindrical section is shorter, usually 0.6 to 0.75 inches (15 to 19 mm). The use of interchangeable chokes allows tuning the performance of a given combination of shotgun and shotshell to achieve a desired level of performance.
==Function==
A choke is designed to alter the distribution of the shot as it leaves the firearm. For shooting most game birds and clay pigeons, a desirable pattern is one that is as large as possible while being dense enough to ensure multiple hits on the target. Shotguns intended for defensive use often have cylinder or improved cylinder chokes for the widest shot pattern at typically short defensive ranges. The choke should be tailored to the range and size of the targets. A skeet shooter shooting at close targets might use 0.005 inches (127 micrometres) of constriction to produce a 30 inch (76 cm) diameter pattern at a distance of 21 yards (19 m). A trap shooter shooting at distant targets might use 0.030 inches (762 micrometres) of constriction to produce a 30 inch (76 cm) diameter pattern at 40 yards (37 m). Special chokes for turkey hunting, which requires long range shots at the small head and neck of the bird, can go as high as 0.060 inches (1500 micrometres). The use of too much choke and a small pattern increases the difficulty of hitting the target; the use of too little choke produces large patterns with insufficient pellet density to reliably break targets or kill game. "Cylinder barrels" have no constriction. See also: Slug barrel
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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