choke tubes

A choke is a tapered constriction of a firearm barrel at its muzzle end. Chokes are most commonly seen on shotguns, but are also used on some rifles, pistols, or even airguns. Notably, some .22 LR match rifles have a constricted bore diameter near the muzzle.Chokes are almost always used with modern hunting and target shotguns to improve performance. Its purpose is to shape the spread of the shot "cloud" or "string" to gain better range and accuracy, and to deliver the optimum pattern of pellet density, for the particular target, depending on its size, range, aspect and whether it is traveling towards, across or away from the shooter. Chokes are implemented as either screw-in chokes, selected for particular applications, or as fixed, permanent chokes, integral to the shotgun barrel.
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
15 to 19 mm (0.6 to 0.75 inches).

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