Editing Shotgun (section)

==Design factors==

===Action===
The [[action (firearms)|action]] is the operating mechanism of a gun. There are many types of shotguns, typically categorized by the number of [[gun barrel|barrel]]s or the way the gun is reloaded.

====Break-action====
{{Main|Double-barreled shotgun}}

[[File:دولول سوار و بغل در یک قاب.jpg|thumb|A view of the [[break-action]] of a side-by-side, and an over-and-under double-barrelled shotgun, both shown with the action open]]

For most of the history of the shotgun, the breechloading [[break-action]] shotgun was the most common type, and double-barreled variants are by far the most commonly seen in modern days. These are typically divided into two subtypes: the traditional "side-by-side" shotgun features two barrels mounted horizontally beside each other (as the name suggests), whereas the "over-and-under" shotgun has the two barrels mounted vertically one on top of the other. Side-by-side shotguns were traditionally used for hunting and other sporting pursuits (early long-barreled side-by-side shotguns were known as "fowling pieces" for their use hunting ducks and other [[waterbird]]s as well as some [[landfowl]]s), whereas over-and-under shotguns are more commonly associated with recreational use (such as [[clay pigeon shooting]]). Both types of double-barrel shotgun are used for hunting and sporting use, with the individual configuration largely being a matter of personal preference.

Another, less commonly encountered type of break-action shotgun is the [[combination gun]], which is an over-and-under design with one smoothbore barrel and one rifle barrel (more often with a rifle barrel on top, but a rifle barrel on bottom was not uncommon). There is also a class of break-action guns called ''[[drilling (firearm)|drillings]]'', which contain three barrels, usually two smoothbore barrels of the same gauge and a rifled barrel, though the only common theme is that at least one barrel be smoothbore. The most common arrangement was essentially a side-by-side shotgun with the rifled barrel below and centered. Usually a drilling containing more than one rifled barrel would have both rifled barrels in the same [[caliber]], but examples do exist with different caliber barrels, usually a [[.22 long rifle]] and a [[centerfire]] cartridge. Although very rare, drillings with three and even four (a ''vierling'') shotgun barrels were made.

====Pump-action====
[[File:Repeterhagelgevär - Livrustkammaren - 98434 (cropped).jpg|thumb|left|upright=1.35|A [[Winchester M1897]], one of the first successful pump-action shotgun designs]]
In [[pump-action shotgun]]s, a linearly sliding [[forearm (firearm component)|fore-end]] [[handguard]] (i.e. ''pump'') is manually moved back-and-forth like a [[bicycle pump#Hand pump|hand pump]] to work the action, extracting the spent shell and inserting a new round, while cocking the [[hammer (firearms)|hammer]] or [[firing pin|striker]]. A pump-action shotgun is typically fed from a [[tubular magazine]] underneath the barrel, which also serves as a [[guide rail]] for the pump. The rounds are fed in one by one through a port in the receiver, where they are lifted by a lever called the ''elevator'' and pushed forward into the chamber by the bolt. A pair of latches at the rear of the magazine hold the rounds in place and facilitate feeding of one shell at a time. If it is desired to load the gun fully, a round may be loaded through the ejection port directly into the chamber, or cycled from the magazine, which is then topped off with another round. Well-known examples include the [[Winchester Model 1897]], [[Remington 870]], and [[Mossberg 500]]/590.

Pump-action shotguns are common hunting, fowling and sporting shotguns. Hunting models generally have a barrel between {{cvt|600|and(-)|700|mm}}. Tube-fed models designed for hunting often come with a dowel rod or other stop that is inserted into the magazine and reduces the capacity of the gun to three shells (two in the magazine and one chambered) as is mandated by U.S. federal law when hunting migratory birds. They can also easily be used with an empty magazine as a single-shot weapon, by simply dropping the next round to be fired into the open ejection port after the spent round is ejected. For this reason, pump-actions are commonly used to teach novice shooters under supervision, as the trainer can load each round more quickly than with a break-action, while unlike a break-action the student can maintain his grip on the gun and concentrate on proper handling and firing of the weapon.

Pump-action shotguns with shorter barrels and little or no barrel choke are highly popular for use in home defense, military and law enforcement, and are commonly known as [[riot shotgun|riot guns]]. The minimum barrel length for shotguns in most of the U.S. is {{convert|18|in|mm}}, and this barrel length (sometimes {{convert|18.5|-|20|in|mm|abbr=on}} to increase magazine capacity and/or ensure the gun is legal regardless of measuring differences<ref>{{cite web |url=http://www.mossberg.com/products/default.asp?id=5&display=specs |title=Mossberg & Sons &#124; Products |publisher=Mossberg.com |access-date=19 February 2015 |url-status=dead |archive-url=https://web.archive.org/web/20120814015009/http://www.mossberg.com/products/default.asp?id=5&display=specs |archive-date=14 August 2012 }}</ref>) is the primary choice for riot shotguns. The shorter barrel makes the weapon easier to maneuver around corners and in tight spaces, though slightly longer barrels are sometimes used outdoors for a tighter spread pattern or increased accuracy of slug projectiles. Home-defense and law enforcement shotguns are usually chambered for 12-gauge shells, providing maximum shot power and the use of a variety of projectiles such as buckshot, rubber, sandbag and slug shells, but 20-gauge (common in bird-hunting shotguns) or .410 (common in youth-size shotguns) are also available in defense-type shotgun models allowing easier use by novice shooters.

A riot shotgun has many advantages over a handgun or rifle. Compared to "defense-caliber" handguns (chambered for [[9mm Parabellum]], [[.38 Special]], [[.357 Magnum]], [[.40 S&W]], [[.45 ACP]] and similar), a shotgun has far more power and damage potential (up to 10 times the muzzle energy of a [[.45 ACP]] cartridge), allowing a "[[stopping power|one-shot stop]]" that is more difficult to achieve with typical handgun loads. Compared to a rifle, riot shotguns are easier to maneuver due to the shorter barrel, still provide better damage potential at indoor distances (generally 3–5 meters/yards), and reduce the risk of "overpenetration"; that is, the bullet or shot passing completely through the target and continuing beyond, which poses a risk to those behind the target through walls. The wide spread of the shot reduces the importance of shot placement compared to a single projectile, which increases the effectiveness of "point shooting" – rapidly aiming simply by pointing the weapon in the direction of the target. This allows easy, fast use by novices.

====Lever-action====
[[File:M1887 LH.JPG|thumb|upright=1.35|A modern reproduction of the [[Winchester M1887]] lever-action shotgun]]
Early attempts at repeating shotguns invariably centred around either bolt-or [[lever-action]] designs, drawing inspiration from contemporary repeating rifles, with the earliest successful repeating shotgun being the lever-action [[Winchester M1887]], designed by John Browning at the behest of the Winchester Repeating Arms Company.

Lever shotguns, while less common, were popular in the late 19th century with the Winchester Model 1887 and Model 1901 being prime examples. Initially very popular, demand waned after the introduction of pump-action shotguns around the start of the 20th century, and production was eventually discontinued in 1920.

One major issue with lever-actions (and to a lesser extent pump-actions) was that early shotgun shells were often made of paper or similar fragile materials (modern hulls are plastic or metal). As a result, the loading of shells, or working of the action of the shotgun, could often result in cartridges getting crushed and becoming unusable, or even damaging the gun.

Lever shotguns have seen a return to the gun market in recent years, however, with Winchester producing the Model 9410 (chambering the .410 gauge shotgun shell and using the action of the Winchester Model 94 series lever-action rifle, hence the name), and a handful of other firearm manufacturers (primarily [[Norinco]] of China and [[ADI Ltd.]] of Australia) producing versions of the Winchester Model 1887/1901 designed for modern 12-gauge [[smokeless powder|smokeless]] shotshells with more durable plastic casings. There has been a notable increase in lever-action shotgun sales in Australia since 1997, when pump-actions were effectively outlawed.

====Bolt-action====
[[Bolt-action]] shotguns, while uncommon, do exist. One of the best-known examples is a 12-gauge manufactured by Mossberg featuring a 3-round magazine, marketed in Australia just after changes to the gun laws in 1997 heavily restricted the ownership and use of pump-action and semi-automatic shotguns. They were not a huge success, as they were somewhat slow and awkward to operate, and the rate of fire was noticeably slower (on average) than a double-barrelled gun. The [[Rifle Factory Ishapore]] in India also manufactured a single-shot [[.410 bore]] shotgun based on the [[Lee–Enfield|SMLE Mk III*]] rifle. The Russian Berdana shotgun was effectively a single-shot bolt-action rifle that became obsolete, and was subsequently modified to chamber 16-gauge shotgun shells for civilian sale. The U.S. military [[M26 Modular Accessory Shotgun System|M26]] is also a bolt-action weapon. Bolt-action shotguns have also been used in the "goose gun" application, intended to kill birds such as [[geese]] at greater range. Typically, goose guns have long barrels (up to 36&nbsp;inches), and small bolt-fed magazines. Bolt-action shotguns are also used in conjunction with slug shells for the maximum possible accuracy from a shotgun.<ref>{{cite web|url=http://www.gun-tests.com/performance/apr97browning.html |title=April, 97 Browning |publisher=Gun-tests.com |access-date=5 September 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080725055416/http://www.gun-tests.com/performance/apr97browning.html |archive-date=25 July 2008}}</ref>

In Australia, some straight-pull bolt-action shotguns, such as the Turkish-made Pardus BA12 and Dickinson T1000, the American [[M26 Modular Accessory Shotgun System|C-More Competition M26]], as well as the indigenous-designed SHS STP 12, have become increasingly popular alternatives to lever-action shotguns, largely due to the better ergonomics with less stress on the shooter's trigger hand and fingers when cycling the action.

====Revolver====
[[File:MC255-2.jpg|thumb|Closeup of MTs255]]
Colt briefly manufactured several revolving shotguns that were not particularly successful. The [[Colt Model 1839 Shotgun]] was manufactured between 1839 and 1841. Later, the Colt Model 1855 Shotgun, based on the [[Colt revolving rifle|Model 1855 revolving rifle]], was manufactured between 1860 and 1863. Because of their low production numbers and age they are among the rarest of all Colt firearms.<ref name="Sapp2007">{{cite book|last=Sapp|first=Rick|title=Standard Catalog of Colt Firearms|url=https://books.google.com/books?id=6eBW-HqX24cC&pg=PA209|year=2007|publisher=Gun Digest Books|location=Iola, Wisconsin|isbn=978-1-4402-2697-7|pages=198, 209}}</ref>

The [[Armsel Striker]] was a modern take on the revolving shotgun that held ten rounds of 12-gauge ammunition in its cylinder. It was copied by [[Cobray]] as the Streetsweeper.<ref name="Cutshaw2011">{{cite book|last=Cutshaw|first=Charles Q.|title=Tactical Small Arms of the 21st Century: A Complete Guide to Small Arms From Around the World|url=https://books.google.com/books?id=55szjc6g520C&pg=PA50|year=2011|publisher=Gun Digest Books|location=Iola, Wisconsin|isbn=978-1-4402-2709-7|page=50}}</ref><ref name="JonesWhite2008">{{cite book|last1=Jones|first1=Richard D.|last2=White|first2=Andrew|title=Jane's Guns Recognition Guide 5e|url=https://books.google.com/books?id=xNa3OtG25a0C&pg=PA355|date=27 May 2008|publisher=HarperCollins|isbn=978-0-06-137408-1|page=355}}</ref>

Taurus manufactures a carbine variant of the [[Taurus Judge]] revolver along with its Australian partner company [[Rossi (manufacturer)|Rossi]], known as the ''Taurus/Rossi Circuit Judge''. It comes in the original combination chambering of [[.410 bore]] and [[.45 Long Colt]], as well as the [[.44 Remington Magnum]] chambering. The rifle has small blast shields attached to the cylinder to protect the shooter from hot gases escaping between the cylinder and barrel.<ref name="Muramatsu2013">{{cite book|last=Muramatsu|first=Kevin|title=The Gun Digest Book of Centerfire Rifles Assembly/Disassembly|url=https://books.google.com/books?id=uDImaye2tY0C&pg=PA310|year=2013|publisher=Krause Publications|location=Iola, Wisconsin|isbn=978-1-4402-3544-3|page=310}}</ref>

The [[MTs255]] ({{langx|ru|link=no|МЦ255}}) is a shotgun fed by a 5-round internal [[revolver|revolving]] cylinder. It is produced by the [[TsKIB SOO]], Central Design and Research Bureau of Sporting and Hunting Arms. They are available in 12, 20, 28 and 32 gauges, and .410 bore.

====Semi-automatic====
{{main|Semi-automatic shotgun}}

[[File:Browning Auto-5 20g Mag.jpg|thumb|left|upright=1.35|A [[Browning A-5]] semi-automatic shotgun]]

[[Recoil operation|Recoil]]/[[recoil operation#Inertia|inertia-driven]] or [[gas-operated]] actions are other popular methods of increasing the rate of fire of a shotgun; these [[semi-automatic firearm|self-loading]] shotguns are generally referred to as ''autoloaders''. Instead of having the action manually operated by a pump or lever, the action automatically cycles each time the shotgun is fired, ejecting the spent shell and reloading a fresh one into the chamber. The first successful semi-automatic shotgun was [[John Browning]]'s [[Auto-5]], first produced by [[Fabrique Nationale]] beginning in 1902. Other well-known examples include the [[Remington 1100]], [[Benelli M1]], and [[Saiga-12]].

Some, such as the [[Franchi SPAS-12]] and [[Benelli M3]], are capable of switching between semi-automatic and pump action. These are popular for two reasons; first, some jurisdictions forbid the use of semi-automatic actions for hunting, and second, lower-powered rounds, like "reduced-recoil" buckshot shells and many [[less-lethal]] cartridges, have insufficient power to reliably cycle a semi-automatic shotgun.

====Automatic====
Fully [[automatic shotgun]]s, such as the 1960s (appeared in 1967) Vietnam War era Remington Model 7188 (designed for and used by US Navy SEALs in Vietnam), the [[Auto Assault-12]] (AA-12) or the [[Daewoo Precision Industries USAS-12|USAS-12]] also exist, but they are still rare.

====Other====

In addition to the commonly encountered shotgun actions already listed, there are also shotguns based on the [[Martini-Henry]] rifle design, originally designed by British arms maker [[W.W. Greener]].

Some of the more interesting advances in shotgun technology include the versatile [[NeoStead 2000]] and fully automatics such as the [[Pancor Jackhammer]] or [[Atchisson Assault Shotgun|Auto-Assault 12]].

In 1925, Rodolfo Cosmi produced the first working [[prototype]] hybrid semi-automatic shotgun, which had an 8-round magazine located in the stock. While it reloaded automatically after each shot like a semi-automatic, it had a break-action to load the first shell. This design has only been repeated once, by Beretta with their UGB25 automatic shotgun. The user loads the first shell by breaking the gun in the manner of a break-action shotgun, then closes it and inserts the second shell into a clip on the gun's right side. The spent hulls are ejected downwards. The guns combine the advantages of the break action (they can be proven to be safe by breaking open, there are no flying hulls) with those of the semi-automatic (low recoil, low barrel axis position hence low muzzle flip).

The Italian firearms manufacturer [[Benelli Armi SpA]] also makes the [[Benelli M3]], a dual-mode hybrid shotgun that allows the user the choice of semi-automatic or pump-action operation. Pump-action operation is employed when shooting less [[muzzle energy|energetic]] shells (such as [[baton round]]s) that do not generate enough [[recoil]] to operate the semi-automatic mechanism. Conversely, the semi-automatic mode can be employed with more powerful shells, absorbing some of the recoil. Switching between the two modes is done by manipulating the ring located at the front of the [[foregrip]].

The French firearm manufacturer [[Verney-Carron]] produces the Véloce shotgun, a "lever-release blowback firearm" using [[bolt (firearms)|bolt]] catch mechanism like its similarly designed SpeedLine rifle. The Véloce is in essence a modified inertia-driven semi-automatic shotgun, but after [[blowback (firearms)|blowback]] the bolt is trapped by a bolt stop and cannot return to battery unless it is manually released by depressing a thumb lever near the tang of the grip. Because the gun will not chamber a new round without manual actuation, the design is technically not really a self-loading, and Verney-Carron described it as a "manual repeating shotgun". When Australian [[gun shop|firearm dealer]]s tried to import the Véloce shotgun in 2018, [[Australian Greens|Greens]]' [[David Shoebridge]] and [[gun control|anti-gun]] groups such as [[Gun Control Australia]] caused a [[moral panic]] on the [[mainstream media]], calling it "semi-semi-automatic" that needed to be prohibited as a "rapid-fire weapon".<ref>{{cite web|url=https://davidshoebridge.org.au/2018/06/08/media-release-new-semi-semi-automatic-firearms-fresh-risk-to-public-safety/|title=New "semi-semi-automatic" firearms fresh risk to public safety|publisher=David Shoebridge – Media release|date=8 June 2018|access-date=13 December 2020|archive-date=29 October 2020|archive-url=https://web.archive.org/web/20201029102529/https://davidshoebridge.org.au/2018/06/08/media-release-new-semi-semi-automatic-firearms-fresh-risk-to-public-safety/|url-status=dead}}</ref><ref>{{cite news|url=https://www.abc.net.au/news/2018-05-30/push-to-import-rapid-fire-shotgun-to-australia-sparks-concerns/9807790|title=Push to import new 'rapid-fire' shotgun into Australia sparks concerns|last=Carbonell|first=Rachel|newspaper=ABC News|date=30 May 2018|access-date=13 December 2020}}</ref><ref>{{cite web|url=https://www.theguardian.com/australia-news/2018/may/30/calls-to-ban-verney-carrons-fast-lever-action-rifle-in-australia|title=Calls to ban Verney-Carron's fast lever action rifle in Australia|last=Wahlquist|first=Calla|work=The Guardian|date=30 May 2018|access-date=13 December 2020}}</ref><ref>{{cite web|url=https://ssaa.org.au/news-resources/politics/french-hunting-shotgun-choking-on-red-tape|title=French hunting shotgun choking on red tape|publisher=Sporting Shooters' Association of Australia|date=7 June 2018|access-date=13 December 2020}}</ref>

=== Gauge ===<!-- Other articles link here -->
[[File:Shotgun.jpg|thumb|right|A [[United States Army]] soldier armed with a [[Mossberg 500]] shotgun]]
{{Main|Gauge (firearms)}}
The gauge number is determined by the weight, in fractions of a pound, of a solid sphere of lead with a diameter equal to the inside diameter of the barrel. So, a 10-gauge shotgun nominally should have an inside diameter equal to that of a sphere made from one-tenth of a pound of lead. Each gauge has a set [[caliber]]. By far the most common gauges are 12 (0.729 in, 18.5mm diameter) and 20 (0.614 in, 15.6mm), this includes other more or less common gauges, such as the 10, 16, 24, 28, 32, and 67 ([[.410 bore]]) gauge.

Different gauges have different typical applications. 12-gauge shotguns are common for hunting geese, large ducks, or other big larger gamebirds; professional skeet and trap shooting; military applications; and home-defense applications. 16-gauge shotguns were once common for hunters who wanted to use only a single shotgun for gamebirds normally pursued with 12 or 20-gauge shotguns, but have become rarer in recent years. 20-gauge shotguns are often used for gamebirds such as doves, smaller ducks, and quail. 28-gauge shotguns are not as common, but are classic quail-hunting guns. .410 gauge shotguns are typically used for squirrel hunting or for sportsmen seeking the challenge of killing game with a smaller load.

Other, less common shotgun cartridges have their own unique uses. Ammunition manufacturer CCI produces 9mm Parabellum (.355 in.) and several other popular pistol calibers up to .45 ACP (11.43mm), as well as smaller calibers such as .22 Long Rifle (5.5mm) and .22 Magnum (5.5mm). These are commonly called snake shot cartridges.<ref>{{cite book|author=Hearst Magazines|title=Popular Mechanics|url=https://books.google.com/books?id=0N4DAAAAMBAJ&pg=PA197|date=October 1947|publisher=Hearst Magazines|page=197}}</ref> Larger gauges, up to 4 bore, too powerful to shoulder, have been built, but were generally affixed to small boats and referred to as [[punt gun]]s. These were used for commercial [[Anatidae|waterfowl]] hunting, to kill large numbers of birds resting on the water.

[[File:Bond Arms Texas Defender Cowboy .45 .410.JPG|thumb|Bond Arms Cowboy Defender .45 Colt/.410 Shotshell Derringer]]
Handguns have also been produced that are capable of firing either .45 (Long) Colt or .410 shotgun shells from the same chamber; they are commonly known as "snake guns". [[Derringer]]s such as the "[[Bond Arms|Snake Slayer and Cowboy Defender]]" are popular among some outdoors-men in the South and Southwest regions of the United States. There are also some revolvers, such as the [[Taurus Judge]] and [[Smith & Wesson Governor]], that are capable of shooting the [[.45LC]]/.410 rounds; but as with derringers they are not considered shotguns.

The [[.410 bore]] (10.4&nbsp;mm) is unusual, being measured in inches, and would be approximately 67 "real" gauge, though its short hull versions are nominally called 36-gauge in Europe. It uses a relatively small charge of shot. It is used for hunting and for skeet. Because of its very light recoil (approx 10 N), it is often used as a beginner's gun. However, the small charge and typically tight choke make it more difficult to hit targets. It is also frequently used by expert shooters because of the difficulty, especially in expensive side by side and over/under models for hunting small bird game such as quail and doves.<ref>{{cite web|url=http://www.chuckhawks.com/410bore.htm |title=410 Gauge |publisher=Chuckhawks.com |access-date=19 February 2015}}</ref> Inexpensive bolt-action .410 shotguns are a very common first hunting shotgun among young pre-teen hunters, as they are used mostly for hunting squirrels, while additionally teaching bolt-action manipulation skills that will transfer easily later to adult-sized hunting rifles. Most of these young hunters move up to a [[20-gauge shotgun|20-gauge]] within a few years, and to 12-gauge shotguns and full-size hunting rifles by their late teens. Still, many who are particularly recoil-averse choose to stay with 20-gauge shotguns all their adult life, as it is a suitable gauge for many popular hunting uses.

A recent innovation is the back-boring of barrels, in which the barrels are bored out slightly larger than their actual gauge. This reduces the compression forces on the shot when it transitions from the chamber to the barrel. This leads to a slight reduction in perceived recoil, and an improvement in shot pattern due to reduced deformation of the shot.

===Shot===
[[File:USMC-05459.jpg|thumb|U.S. Marines fire their shotguns]]
Most shotguns are used to fire "a number of ball shot", in addition to slugs and sabots. The ball shot or pellets is for the most part made of lead but this has been partially replaced by bismuth, steel, tungsten-iron, tungsten-nickel-iron and even tungsten polymer loads. Non-toxic loads are required by Federal law for [[waterfowl hunting]] in the US, as the shot may be ingested by the waterfowl, which some authorities believe can lead to health problems due to the lead exposure. Shot is termed either [[birdshot]] or [[buckshot]] depending on the shot size. Informally, birdshot pellets have a diameter smaller than {{convert|5|mm|in|abbr=on}} and buckshot are larger than that. Pellet size is indicated by a number; for bird shot this ranges from the smallest 12 (1.2&nbsp;mm, 0.05 in) to 2 (3.8&nbsp;mm, 0.15 in) and then BB (4.6&nbsp;mm, 0.18 in).<ref>{{cite book|author=Hearst Magazines|title=Popular Mechanics|url=https://books.google.com/books?id=0N4DAAAAMBAJ&pg=PA196|date=October 1947|publisher=Hearst Magazines|page=196}}</ref>

For buckshot, the numbers start and end with 4, 3, 2, 1, 0 ("single-aught"), 00 ("double-aught"), 000 ("triple-aught"), and 0000 ("quadruple-aught"). A different informal distinction is that "bird shot" pellets are small enough that they can be measured into the cartridge by weight, and simply poured in, whereas "buckshot" pellets are so large they must be stacked inside the cartridge in a fixed geometric arrangement to fit. The diameter in hundredths of an inch of bird shot sizes from No. 9 to No. 1 can be obtained by subtracting the shot size from 17. Thus, No. 4 bird shot is 17 – 4 = 13 = {{convert|0.13|in|mm}} in diameter. Different terminology is used outside the United States. In England and Australia, for example, 00 buckshot cartridges are commonly referred to as "[[Buckshot|S.G.]]" (Swanshot gauge) cartridges.

{| class="wikitable" style="text-align:center;"
|+ Table of American standard birdshot size
|-
!Size
![[Caliber]]
!Pellets/10 g lead
!Pellets/10 g steel
|-
| FF|| 5.84&nbsp;mm (.230")|| 8 || 12
|-
| F|| 5.59&nbsp;mm (.220")|| 10 || 14
|-
| TT|| 5.33&nbsp;mm (.210")|| 11 || 16
|-
| T|| 5.08&nbsp;mm (.200")|| 13 || 19
|-
| BBB|| 4.83&nbsp;mm (.190")|| 15 || 22
|-
| BB|| 4.57&nbsp;mm (.180")|| 18 || 25
|-
| B|| 4.32&nbsp;mm (.170")|| 21 || 30
|-
| 1|| 4.06&nbsp;mm (.160")|| 25  || 36
|-
| 2|| 3.81&nbsp;mm (.150")|| 30 || 44
|-
| 3|| 3.56&nbsp;mm (.140")|| 37  || 54
|-
| 4|| 3.30&nbsp;mm (.130")|| 47 || 68
|-
| 5|| 3.05&nbsp;mm (.120")|| 59 || 86
|-
| 6|| 2.79&nbsp;mm (.110")|| 78 || 112
|-
| 7|| 2.41&nbsp;mm (.100")|| 120 || 174
|-
| 8|| 2.29&nbsp;mm (.090")|| 140 || 202
|-
| 9|| 2.03&nbsp;mm (.080")|| 201 || 290
|}

{| class="wikitable" style="text-align:center;"
|+ Table of buckshot size
|-
!Size
![[Caliber]]
!Pellets/10 g lead
|-
| 000 or LG ("triple-aught")|| 9.1&nbsp;mm (.36")|| 2.2
|-
| 00 or SG ("double-aught")|| 8.4&nbsp;mm (.33")|| 2.9
|-
| 0 ("one-aught")|| 8.1&nbsp;mm (.32")|| 3.1
|-
| 1|| 7.6&nbsp;mm (.30")|| 3.8
|-
| 2 or SSG|| 6.9&nbsp;mm (.27")|| 5.2
|-
| 3|| 6.4&nbsp;mm (.25")|| 6.6
|-
| 4|| 6.1&nbsp;mm (.24")|| 7.4
|}

===Pattern and choke===<!-- This section is linked from [[Flintlock]] -->
{{main|Choke (firearms)}}
{{See also|Slug barrel}}
Shot, small and round and delivered without spin, is ballistically inefficient. As the shot leaves the barrel it begins to disperse in the air. The resulting cloud of pellets is known as the shot [[pattern]], or [[shotgun shot spread]]. The ideal pattern would be a circle with an even distribution of shot throughout, with a density sufficient to ensure enough pellets will intersect the target to achieve the desired result, such as a kill when hunting or a break when shooting clay targets. In reality the pattern is closer to a [[Normal distribution|Gaussian]], or normal distribution, with a higher density in the center that tapers off at the edges. Patterns are usually measured by firing at a {{convert|30|in|cm|adj=on}} diameter circle on a large sheet of paper placed at varying distances. The hits inside the circle are counted, and compared to the total number of pellets, and the density of the pattern inside the circle is examined. An "ideal" pattern would put nearly 100% of the pellets in the circle and would have no voids—any region where a target silhouette will fit and not cover 3 or more holes is considered a potential problem.

A constriction in the end of the barrel known as the [[Choke (firearms)|choke]] is used to tailor the pattern for different purposes. Chokes may either be formed as part of the barrel at the time of manufacture, by squeezing the end of the bore down over a [[mandrel]], or by threading the barrel and screwing in an interchangeable choke tube. The 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, a maker of interchangeable shotgun chokes, uses a conical portion about three times the bore diameter in length, so the shot is gradually squeezed down with minimal deformation. The cylindrical section is shorter, usually {{convert|0.6|to|0.75|in|mm|abbr=off}}. The use of interchangeable chokes has made it easy to tune the performance of a given combination of shotgun and shotshell to achieve the desired performance.

The choke should be tailored to the range and size of the targets. A skeet shooter shooting at close targets might use 127 micrometres (0.005&nbsp;inches) of constriction to produce a {{convert|76|cm|in|abbr=on}} diameter pattern at a distance of {{convert|19|m|yd|abbr=on}}. A [[trap shooting|trap]] shooter shooting at distant targets might use 762 micrometres (0.030&nbsp;inches) of constriction to produce a {{convert|76|cm|in|abbr=on}} diameter pattern at {{convert|37|m|yd|abbr=on}}. Special chokes for turkey hunting, which requires long range shots at the small head and neck of the bird, can go as high as 1500 micrometres (0.060&nbsp;inches). The use of too much choke and a small pattern increases the difficulty of hitting the target, whereas 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.

{| class="wikitable" style="text-align:center;"
|+ Table of shotgun chokes<br />for a 12-gauge shotgun using lead shot
|-
!Constriction<br />(micrometres)
!Constriction<br />(inches)
!American name
!British name
!Percentage of shot<br />in a {{convert|76|cm|in|abbr=on}} circle <br />at {{convert|37|m|yd|abbr=on}}
!Total spread at 37 m <br /> (cm)
!Total spread at 40 yds <br /> (in)
!Effective range<br /> (m)
!Effective range<br /> (yd)
|-
| 0|| .000|| Cylinder|| || 40|| 150|| 59|| 18||20
|-
| 127|| .005|| Skeet|| {{frac|1|8}}|| 45|| 132|| 52|| 21||23
|-
| 254|| .010|| Improved Cylinder|| {{frac|1|4}}|| 50|| 124|| 49|| 23||25
|-
| 381|| .015|| Light Modified|| || &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;
|-
| 508|| .020|| Modified|| {{frac|1|2}}|| 60|| 117|| 46|| 32||35
|-
| 635|| .025|| Improved Modified|| {{frac|3|4}}|| &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;
|-
| 762|| .030|| Light Full|| || &nbsp;|| 109|| 43|| &nbsp; || &nbsp;
|-
| 889|| .035|| Full|| Full|| 70|| &nbsp;|| &nbsp;|| 37||40
|-
| 1143|| .045|| Extra Full|| || &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;
|-
| 1270|| .050|| Super Full|| || &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;|| &nbsp;
|}

Other specialized choke tubes exist as well. Some turkey hunting tubes have constrictions greater than "Super Full", 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 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 1 in 36&nbsp;cm twist, 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 shotgun]]s, primarily those of the [[Vietnam War]] era. They were available for aftermarket addition in the 1970s from companies like A & W Engineering.<ref>{{cite book|title=The Police Shotgun Manual|publisher=Thomas|author=Roger H. Robinson|year=1973|isbn=978-0-398-02630-1|pages=91–94}}</ref> 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 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.

===Barrel length===
{{see|Sawed-off shotgun|Coach gun|Punt gun}}

Shotguns generally have longer barrels than modern rifles. Unlike rifles, however, the long shotgun barrel is not for ballistic purposes; shotgun shells use small powder charges in large diameter bores, and this leads to very low muzzle pressures (see [[internal ballistics]]) and very little velocity change with increasing barrel length. According to Remington, modern powder in a shotgun burns completely in {{cvt|25|to(-)|36|cm|0}} barrels.

Since shotguns are generally used for shooting at small, fast moving targets, it is important to ''lead'' the target by firing slightly ahead of the target, so that when the shot reaches the range of the target, the target will have moved into the pattern.

Shotguns made for close ranges, where the angular speed of the targets is great (such as skeet or upland bird hunting), tend to have shorter barrels, around {{convert|24|to(-)|28|in|cm}}. Shotguns for longer range shooting, where angular speeds are small (trap shooting; quail, pheasant, and waterfowl hunting), tend to have longer barrels, 28 to {{convert|36|in|cm}}. The longer barrels have more [[angular momentum]], and will therefore swing more slowly but more steadily. The short, low angular momentum barrels swing faster, but are less steady. These lengths are for pump or semi-auto shotguns; break open guns have shorter overall lengths for the same barrel length, and so will use longer barrels. The break open design saves between {{cvt|3|and(-)|6|in|cm|0|order=flip}} in overall length, but in most cases pays for this by having two barrels, which adds weight at the muzzle. Barrels for shotguns have been getting longer as modern steels and production methods make the barrels stronger and lighter; a longer, lighter barrel gives the same inertia for less overall weight.

Shotguns for use against larger, slower targets generally have even shorter barrels. Small game shotguns, for hunting game like rabbits and squirrels, or shotguns for use with buckshot for deer, are often {{convert|56|to(-)|61|cm|in|abbr=on}}.

Shotguns intended for all-round hunting are a compromise, but a {{convert|72|to(-)|74|cm|in|abbr=on}} barrel pump-action 12-gauge shotgun with a modified choke can serve admirably for use as one gun intended for general all-round hunting of small-game such as quails, rabbits, pheasants, doves, and squirrels in semi-open wooded or farmland areas in many parts of the eastern US (Kentucky, Indiana, Tennessee) where dense brush is less of a hindrance and the ability to have more reach is important. For hunting in dense brush, shorter barrel lengths are often preferred when hunting the same types of game.

===Caliber conversion sleeves===
Shotguns are well suited for the use of [[caliber conversion sleeve]]s, allowing most single- and double-barrel shotguns to fire a wide range of ammunition.<ref name="soldiersystems.net">http://soldiersystems.net/2012/11/23/x-caliber-survival-rifle-gauge-adapter-system/ X-CALIBER Survival-Rifle Gauge Adapter System</ref><ref>https://www.tactical-life.com/firearms/x-caliber/ X-Caliber X-treme: Multi-Caliber Weapons. NEVER BRING A KNIFE TO A GUNFIGHT. By DENNIS ADLER. FROM...RIFLE FIREPOWER MAGAZINE. 20 December 2013</ref> The [[X Caliber]] system consists of eight adapter sleeves that allow the 12-gauge models to fire: [[.380 ACP]], [[9mm Luger]], [[.38 Special]], [[.357 Magnum]], [[.40 S&W]], [[.44 Special]], [[.44 Magnum]], [[.45 ACP]], [[.45 Long Colt]], [[.410 gauge]] and [[20-gauge]] ammunition. They even make four adapter sleeves that allow the 20-gauge models to fire: 9mm Luger, .38 Special, .357 Magnum, .45 ACP, .45 Long Colt, and .410 gauge ammunition.