Choke (firearms)
A choke is a tapered constriction of a
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.[2] 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 (0.6 to 0.75 inches) in diameter.
Function
A choke is designed to alter or shape the distribution of the shot as it leaves the firearm. For shooting most
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.[3]
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.[4]
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.[5]
The first known patents for choke boring were granted Sylvester H. Roper, an American inventor and gunsmith.[6] 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.[7]
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 (large bores, any boring), Class 2 (choke bores, 12 gauge), Class 3 (guns of English boring or cylinders) and Class 4 (small gauges, any boring). 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
Constriction
The exit end of a choke is smaller by some dimension than the actual
Generally the constriction ranges for chokes will be 0.00-1.15 mm (0.00-0.045 inch) while the constriction for relatively common turkey chokes may be as much as 2.50 mm (0.10 inch). Choke is measured experimentally by observing the percentage of pellets in a charge that impact inside a 75 cm circle at 35 m (25 m for "cylinder" and "Skeet").[8] Although different choke manufacturers have different identification of their chokes, the notches in the chart below are generally accepted.[9]
A common method of expressing the amount of constriction is by "points". A "point" is equivalent to 0.025 mm (0.001 in) of constriction of the inner diameter of a choke. Hence, 40 points of constriction would correspond to a constriction of 0.040 inch (≈ 1 mm) in the inner diameter of a choke, corresponding to "Extra Full".
Choke (American designation) |
Constriction | Percentage of lead shot in 75 cm circle at 35 m (30-inch circle at 40 yards) |
Identification (notches) |
Identification (British) |
Identification (stars) (Spanish shotguns) |
---|---|---|---|---|---|
Cylinder (no choke) | 0.00 mm (0 in) | 40% at 35 m (40 yd) 70% at 23 m (25 yd) |
IIIII (5 notches) | ***** (5 stars) | |
Skeet 1 | 0.13 mm (0.005 in) | 45% at 35 m (40 yd) 75% at 23 m (25 yd) |
1/8 | ||
Improved Cylinder | 0.25 mm (0.01 in) | 50% | IIII (4 notches) | 1/4 | **** (4 stars) |
Skeet 2 (light Mod.) | 0.38 mm (0.015 in) | 55% | 3/8 | ||
Modified | 0.51 mm (0.020 in) | 60% | III (3 notches) | 1/2 | *** (3 stars) |
Improved Modified | 0.635 mm (0.025 in) | 65% | II (2 notches) | 3/4 | ** (2 stars) |
Full | 0.76 mm (0.030 in) | 70% | I (1 notch) | 1/1 | * (1 star) |
Extra Full | 1.015 mm (0.040 in) | 73% | I (1 notch) | ||
Turkey | 1.145 mm (0.045 in) plus | 75% plus | I (1 notch) |
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. (The four wider slots present in the exposed rim of the tube are intended for use with a choke wrench, in the event that a choke tube ever becomes stuck in the barrel, and have no relationship to the amount of choke.)
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 (smaller diameter) chokes.[10][11]
Alternative chokes
Other specialized choke tubes exist as well. Some turkey hunting tubes have constrictions greater than "Turkey", or additional features like porting to reduce recoil, or "straight rifling" that is designed to stop any spin that the shot column might acquire when traveling down the barrel. These tubes are often extended tubes, meaning they project beyond the end of the bore, giving more room for things like a longer conical section. Shot spreaders or diffusion chokes work opposite of normal chokes—they are designed to spread the shot more than a cylinder bore, generating wider patterns for very short range use. A basic spreader choke is simply a "choke" with a larger diameter than the barrel; the spreader choke still makes the barrel more restrictive than just having a shorter barrel, but a shorter barrel may not be allowed due to legal restrictions. A number of recent spreader chokes, such as the Briley "Diffusion" line, actually use rifling in the choke to spin the shot slightly, creating a wider spread. The Briley Diffusion uses a 360 mm twist (1:14"), as does the FABARM Lion Paradox shotgun.
Oval chokes, which are designed to provide a shot pattern wider than it is tall, are sometimes found on combat shotguns, primarily those of the Vietnam War era. They were available for aftermarket addition in the 1970s from companies like A & W Engineering.[12] Military versions of the Ithaca 37 with duckbill choke were used in limited numbers during the Vietnam War by US Navy Seals. It arguably increased effectiveness in close range engagements against multiple targets. Two major disadvantages plagued the system. One was erratic patterning. The second was that the shot would spread too quickly providing a very limited effective zone.
Offset chokes, where the pattern is intentionally slightly off of center, are used to change the point of impact. For instance, an offset choke can be used to make a double barrelled shotgun with poorly aligned barrels hit the same spot with both barrels.
For shotguns with fixed chokes integral to the barrel, it is sometimes still possible to change the choke to a tighter choke. This is done by increasing the diameter of the bore inside the barrel for a short length of barrel, while the portion of the barrel and bore nearest the muzzle is left as it was. The effect is to form what is called a "jug choke" or a "reverse choke".[13] This method is sometimes used by gunsmiths to implement a tighter choke on an existing gun without replaceable chokes, and can be done without requiring replacement of a barrel and without installing new screw-in replaceable chokes. Advantages claimed for a "jug choke" include improved patterns, reduction of recoil, and an increase of choke in a shotgun that does not have replaceable choke tubes. When a "jug choke" is implemented in an existing choked barrel, the bore inside the bored-out section of barrel effectively becomes "overbored", and this also typically lessens the amount of shot deformation, thereby increasing the shot pattern density.[7]
Compatibility chart
The following list should only be used as a guide, and there may be exceptions.
Gauge | Choke threads (metric designation) |
Choke threads (imperial designation) |
Manufacturer and type | Comment |
---|---|---|---|---|
10 ga (19.69 mm) |
M22.12×0.794 mm | 0.871"-32 TPI | Remington pro-bore | |
M21.97×0.577 mm | 0.865"-44 TPI | Tru-Choke | ||
12 ga (18.53 mm) |
M20.62×0.794 mm | 0.812"-32 TPI | Winchester Win-choke, Browning Invector, Mossberg Accu-choke, Weatherby IMC, Savage |
Note that although Win and Rem-choke have the same thread pitch, their shapes are different. |
M20.62×0.794 mm | 0.812"-32 TPI | Remington Rem-choke | Note that although Win-choke and Rem-choke have the same thread pitch, their shape are different. | |
M20.83×0.794 mm | 0.820"-32 TPI | Browning Invector plus | ||
M20.574×1 mm | 0.810"-25.4 TPI | Benelli/ Beretta Krieghoff |
||
M20.75×1 mm | 0.817"-25.4 TPI | Hastings choke II barrels | ||
M22.20×0.794 mm | 0.874"-32 TPI | Mossberg Ulti-Mag | ||
M20.19×0.577 mm | 0.795"-44 TPI | Tru-Choke | ||
M19.66×0.577 mm | 0.774"-44 TPI | Tru-Choke thinwall | ||
16 ga (16.83 mm) |
M18.24×0.577 mm | 0.718"-44 TPI | Tru-Choke | |
20 ga (15.63 mm) |
M17.45×0.794 mm | 0.687"-32 TPI | Winchester Win-choke, Browning Invector, Mossberg Accu-choke, Weatherby IMC, Savage |
|
M17.46×0.794 mm | 11/16"-32 TPI (0.697"-32 TPI) |
Remington Rem-choke | ||
M17.15×0.577 mm | 0.675"-44 TPI | Tru-Choke | ||
28 ga (13.97 mm) |
M15.57×0.577 mm | 0.613"-44 TPI | Tru-Choke | |
.410 (10.41 mm) |
M12.14×0.577 mm | 0.478"-44 TPI | Tru-Choke |
Steel shot and alternatives
Older shotgun barrels and chokes were designed for use with lead shot only. Due to changing worldwide waterfowl hunting law restrictions, the use of lead shot has been banned in many parts of the world by international agreement. The reason is that waterfowl hunting with lead shot was identified as a major cause of
In practice, steel shot patterns as much as two chokes tighter for a given amount of constriction. In other words, a choke that patterns "Modified" with lead or bismuth shot would give a "Full" pattern with steel shot. To avoid excessive wear or grooving from occurring within chokes when shooting steel shot, many manufacturers recommend avoiding shooting steel shot in any chokes marked tighter than "Modified", unless the choke tube is specifically marked as being safe for use with steel shot.[17]
See also
References
- ^ Why choke a barrel? | Air gun blog - Pyramyd Air Report
- ^ "Shotgun". (2011). Encyclopædia Britannica. Retrieved February 5, 2011, from Encyclopædia Britannica Online Library Edition
- ^ Mayer, Alfred Marshall (1883). ""Fusil,"+Gave+An+Account+Of+Choke+Boring" "Sport with Gun and Rod in American Woods and Waters".
- ^ "ZADOVKA SYLVESTRA KRNKY 1849".
- ]
- ^ U.S. patent 53,881, Improvement In Revolving Fire-Arms, April 10, 1866; and U.S. patent 79,861, Improvements In Detachable Muzzle For Shot-Guns, dated July 14, 1868
- ^ a b John Robinson (November 2004). "A beginner's guide to shotgun chokes". Australian Shooter. Retrieved 2013-02-15.
- ^ "Expert Advice". Field and Clays. Archived from the original on July 13, 2010. Retrieved January 16, 2010.
- ^ "Choke Identification". January 16, 2010. Archived from the original on December 9, 2012. Retrieved January 16, 2010.
- ^ "Choke Tube Diameter and Constriction Table". ChokeCity. 2021. Retrieved 2021-10-05.
- ^ "Shotgun Choke With Tightest Shot Pattern". ChokeCity. 2021. Retrieved 2020-01-20.
- ISBN 0-398-02630-0.
- ^ "Choke adjusting with Gilchrist Precision Choke Reamer" (PDF). Brownells. 2003. Retrieved 2013-02-15.
- ^ Sanderson, Glen C. and Frank C. Bellrose. 1986. A Review of the Problem of Lead Poisoning in Waterfowl. Illinois Natural History Survey, Champaign, Illinois. Special Publication 4. 34pp. full report from scholar.google.com (cache)
- ^ A.M. Scheuhammer and S. L. Norris. 1996. "The ecotoxicology of lead shot and lead fishing weights" Ecotoxicology Vol. 5 Number 5 pp. 279-295
- ^ WaterfowlChoke, Smith (2021). "5 Reasons Why Steel Shot is Bad For Your Shotgun".
- ^ "Trulock FAQ on Choke Tubes". Archived from the original on 2013-02-25. Retrieved 2013-02-14.