Choke (firearms)
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. Their 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 and usually between 15 and 19 mm in diameter.
Function
A choke is designed to alter or shape 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, at a particular range. The choke should be tailored to the range and size of the targets. Shotguns intended for defensive use often have cylinder or improved cylinder chokes for the widest shot pattern at typically short defensive ranges; "cylinder barrels" have no constriction.A skeet shooter shooting at close crossing targets might use of constriction to produce a diameter pattern at a distance of. A trap shooter shooting at distant targets traveling away from the gun might use of constriction to produce a diameter pattern at. Special chokes for turkey hunting, which requires long range shots at the small head and neck of the bird, can go as high as.
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.
History
As far back as 1787 a Frenchman by the name of M. Magne de Marolles gave an account of choke-boring, though he argued against it.Some sources state that the first pioneer was a Czech named Dominik Brandejs, who made shotguns with a choke in order to reduce the dispersion of shots, but his design was not popular in the 1820s.
The invention of choke boring is usually attributed to American gunsmiths. J.W. Long, in his book American Wildfowling, credits Jeremiah Smith of Southfield, Rhode Island, as the gunsmith who first discovered the concept, as far back as 1827.
The first known patents for choke boring were granted Sylvester H. Roper, an American inventor and gunsmith. This was followed by a patent claim in London by W.R. Pape, an English gun maker, whose patent application was six weeks too late to the 1866 Roper patent.
While American gunsmiths were the pioneers of the choke boring system, they had not really progressed beyond the elementary stage and their choked shotguns would lead, throw irregular patterns, and not shoot straight.
W. W. Greener's first intimation of the choke formation was derived from instructions given in a customer's letter, in early 1874. The customer's instructions described a choke but did not give any details on the size or shape nor how it was to be obtained. Hence, Greener had to conduct many experiments to determine the perfect shape and size of a choke for a given bore. After that, he developed tools to produce the choke bore profile correctly and smoothly. The system of choke boring that he pioneered was so successful that it was later adopted by other manufacturers and hence, some authorities give him the credit for inventing the concept, since his method became the first repeatable method of choke boring. William Wellington Greener is thus widely credited as being the inventor of the first practical choke, as documented in his classic 1888 publication, The Gun and its Development.
In December 1874, the first mention of Greener's choke bore appeared in an article by J.H. Walsh, the editor of Field magazine. The article mentioned the extraordinary shot pattern that the Greener shotgun could produce. The next issue came with an advertisement from Greener, stating that the firm would guarantee that their new guns would shoot a closer pattern than any other manufacturer. The advertisement claimed that Greener 12 bores were warranted to shoot an average pattern of 210, when the best 12 bore gun in the London Gun Trial of 1866 could only average 127. Naturally, the advertisement generated considerable controversy, especially from rival manufacturers of cylinder guns, who refused to believe the numbers quoted in the advertisement.
To resolve the controversy, the editors of Field magazine decided to conduct a public trial in 1875. The London Trial of 1875 pitted choke bores and cylinder guns of various manufacturers in four categories—Class 1, Class 2, Class 3 and Class 4. The choke bored guns performed better than the cylinder guns in all these tests, and W.W. Greener choke bore guns won the class 1, class 2 and class 4 categories. Greener Choke bores also won at the London Gun Trials of 1877 and 1879, and the Chicago Field Gun Trial of 1879. The results of these trials were responsible for making the W.W. Greener name famous, and for confirming the practical advantage of a repeatable method of controlling the performance of a choke on a shotgun.
Use in competition
The choice of choke type has an impact on performance in shooting competitions. At the Shoot-Off at the 2018 Shotgun World Shoot, U.S. shooter Scott Greene and Russian Roman Anikin both fired their last shots almost simultaneously, but Greene had chosen a more constricted barrel choke. This gave a tighter shot pattern and a greater risk of missing, but ultimately led to his target falling faster to win the Shoot-Off.Constriction
The exit end of a choke is smaller by some dimension than the actual bore of the barrel. This difference in diameter is the amount of constriction. For example, for a 12 gauge, the bore diameter of the barrel is nominally, although different manufacturers do vary their as-manufactured bore from this diameter slightly. This is commonly called "overbore", when the as-built diameter exceeds the nominal diameter. The advantages touted for "overbore" are a perceived reduction in recoil and a lessened shot deformation for improving shot patterns.Generally, the constriction ranges for chokes will be, while the constriction for relatively common turkey chokes may be as much as. Choke is measured experimentally by observing the percentage of pellets in a charge that impact inside a 75 cm circle at 35 m. Although different choke manufacturers have different identification of their chokes, the notches in the chart below are generally accepted. One of the reasons these experiments need to be run is that choke constriction is measured in absolute terms rather than relative to the barrel diameter being choked; a.5 mm choke is unlikely to behave identically in both a 19.7 mm barrel loaded with 2.49 mm shot and a 15.6 mm barrel loaded with 4.57 mm shot.
A common method of expressing the amount of constriction is by "points". A "point" is equivalent to of constriction of the inner diameter of a choke. Hence, 40 points of constriction would correspond to a constriction of in the inner diameter of a choke, corresponding to "Extra Full".
| Choke | Constriction | Percentage of lead shot in 75 cm circle at 35 m | Identification | Identification | Identification |
| Cylinder | 40% at 35 m 70% at 23 m | IIIII | ***** | ||
| Skeet 1 | 45% at 35 m 75% at 23 m | 1/8 | |||
| Improved Cylinder | 50% | IIII | 1/4 | **** | |
| Skeet 2 | 55% | 3/8 | |||
| Modified | 60% | III | 1/2 | *** | |
| Improved Modified | 65% | II | 3/4 | ** | |
| Full | 70% | I | 1/1 | * | |
| Extra Full | 73% | I | |||
| Turkey | plus | 75% plus | I |
Markings
The marking is usually stamped on the underside of the barrel for older guns without choke tubes, or is spelled out in abbreviated text on the barrel near the gauge marking.In the case of choke tubes, the amount of choke for each barrel is usually stamped on the side of the choke tube, or there may be thin slots cut in the exposed rim of the tube at the barrel opening with the number of slots corresponding to the number of stars in this table.
For the case of older, side-by-side, Spanish guns, the choke is often marked on the tang of the barrels, becoming exposed when the wooden forearm is removed, after the double barrels are pivoted off of the break-action, such as when performing a field-stripping and cleaning. The manufacturer's mark, along with the proof marks, and the weight of the barrels in grams, and the proof test pressures are also stamped alongside the choke marking on the tang of the barrels, near where the shells are inserted into the barrels.
In practice, choke tubes tighter than "Full", such as "Turkey", are also commonly marked with but a single thin notch on the end of the tube. Hence, to distinguish between "Full" vs. even tighter chokes, such as "Turkey", it becomes necessary to measure the bore exit diameter of the choke tube to determine precisely which choke type is present among the "Full" and tighter chokes.