Shotgun

A shotgun (also known as a fowling piece or scattergun ) is a smooth-bored firearm that is usually designed to be fired from the shoulder, which uses the energy of a fixed shell to fire a number of small spherical pellets called shot or a solid projectile. Shotguns come in a wide variety of sizes, ranging from 5.5 mm (.22 inch ) bores up to 5 cm (2 inch) bores, and in a range of firearm operating mechanisms, including breech loading, double barreled shotguns, pump-action, bolt-action, lever-action, and semi-automatic models.

Since the shot pellets from a shotgun spread upon leaving the barrel, the power of the burning charge is divided among the pellets, which means that the energy of any one ball of shot is fairly low. In a hunting context, this makes shotguns useful primarily for hunting birds and other small game. However, in a military or law enforcement context, the large number of projectiles makes the shotgun useful as a close quarters combat weapon or a defensive weapon. Shotguns are also used for target shooting sports such as skeet, trap, and sporting clay shooting. These involve shooting clay disks, also known as clay pigeons, thrown in various ways.

Precursors to the shotgun, such as the musket were widely used by armies in the 18th century. However, in the 19th century, shotgun-type weapons were largely replaced on the battlefield with rifles, which were more accurate over longer ranges. The decline in military use of shotguns reversed in World War I, when American forces used 12-gauge pump action shotguns in close-quarters trench fighting. Since the end of World War II, the shotgun has remained in use with modern armies mostly in specialist roles, such as door breaching or for naval boarding parties. On the other hand, shotguns have become a standard firearm for law enforcement use in many countries. Police often use specialty less-lethal or non-lethal ammunitions, such as tear gas shells, bean bags, stun rounds, and rubber projectiles.

Characteristics
Shotguns come in a wide variety of forms, from rimfire models with 5.5 mm (.22 inch ) bores up to massive punt guns with 5 cm (2 inch) bores, and in nearly every type of firearm operating mechanism. The common characteristics that make a shotgun unique center around the requirements of firing shot. These features are the features typical of a shotgun shell, namely a relatively short, wide cartridge, with straight walls, and operating at a relatively low pressure.

Ammunition for shotguns is referred to in the USA as shotgun shells, shotshells, or just shells (when it is not likely to be confused with artillery shells). The term cartridges is standard usage in the United Kingdom. Single projectile loads are generally called shotgun slugs or just slugs.

The shot pellets from a shotgun spread upon leaving the barrel which makes it easier to hit small targets at suitable ranges than with a rifle. The shot is usually fired from a smoothbore barrel; another configuration is the rifled slug barrel, which is used to fire a single projectile (though some slugs can also be fired from smoothbore weapons).

Since the power of the burning charge is divided among the pellets, the energy of any one ball of shot is fairly low, making shotguns useful primarily for hunting birds and other small game. However, the large number of projectiles makes the shotgun useful as a close-combat weapon or defensive weapon, where the short range ensures that many of the projectiles of shot will hit the target (see riot shotgun and combat shotgun). The shotgun is a great gun for self dafence.

Uses
The typical use of a shotgun is against small and/or fast moving targets, often taken while in the air. The spreading of the shot allows the user to point the shotgun close to the target, rather than having to aim precisely as in the case of a single projectile. The disadvantages of shot are limited range and limited penetration of the shot, which is why shotguns are used at short ranges, and typically against smaller targets. Larger shot size, up to the extreme case of the single projectile slug load, results in increased penetration, but at the expense of fewer projectiles and lower probability of hitting the target.

Aside from the most common use against small, fast moving targets, the shotgun has several advantages when used against still targets. First, it has enormous stopping power at short range, more than nearly all handguns and comparable to most rifle cartridges. The wide spread of shot produced by the gun makes it easier to aim and to be used by inexperienced marksmen. A typical self-defense load of buckshot contains 8-27 large lead pellets, resulting in many wound tracks in the target. Also, unlike a rifle bullet, each pellet of shot is less likely to penetrate walls and hit bystanders. It is favored by law enforcement for its low penetration and high stopping power.

On the other hand, the hit potential of a defensive shotgun is often overstated. The typical defensive shot is typically taken at very close ranges, at which the shot charge expands no more than a few centimetres. This means the shotgun must still be aimed at the target with some care. Balancing this is the fact that shot spreads further upon entering the target, and the multiple wound channels of a defensive load are far more likely to produce a disabling wound than a rifle or handgun

Sporting


Some of the most common uses of shotguns are the sports of skeet shooting, trap shooting, and sporting clays. These involve shooting clay disks, also known as clay pigeons, thrown in various ways. Both skeet and trap competitions are featured at the Olympic Games.

Hunting
The shotgun is used for bird hunting, although it is also increasingly used in deer hunting in semi-populated areas where the range of the rifle bullet may pose too great a hazard. Many modern smooth bore shotguns using rifled slugs are extremely accurate out to 75 m (80 yards) or more, while the rifled barrel shotgun with the use of sabot slugs are typically accurate to 100 m (110 yards) and beyond -- well within the range of the majority of kill shots by experienced deer hunters using shotguns.

However, given the relatively low muzzle velocity of slug ammunition typically around 500 m/s (about 1600 feet per second) and blunt, poorly streamlined shape of typical slugs (which cause them to lose velocity very rapidly, compared to rifle bullets), a hunter must pay close attention to the ballistics of the particular make of ammunition to ensure a humane killing shot on a deer. Shotguns are normally used to hunt whitetail deer in the thick brush and briars of the south-eastern and upper midwestern US, where, due to the dense cover, ranges tend to be very close--25 m or less. At any reasonable range, shotgun slugs make effective lethal wounds due to their tremendous mass, reducing the length of time that an animal might suffer. A typical 12 gauge shotgun slug is a blunt piece of metal that could be described as a 18 mm (.729) caliber that weighs 28 grams (432 grains); for comparison, a common deer-hunting rifle round is a .308 (7.62 mm) slug weighing 9.7 g (150 grains), however the dynamics of the rifle cartridge allow for a different type of wound, and also a much further reach.

Law enforcement
In the US, law enforcement agencies often use riot shotguns, especially for crowd and riot control where they may be loaded with less-lethal rounds such as rubber bullets or bean bags.

Civilian use
Compared to handguns, shotguns are heavier, larger, and not as maneuverable in close quarters (which also presents a greater retention problem), but do have the following advantages:
 * They are generally much more powerful.
 * They are easier for most shooters to hit with.
 * They are generally perceived as more intimidating.
 * On average, a quality pump-action shotgun is generally less expensive than a quality handgun (self-loading shotguns are generally more expensive than their pump-action counterparts).
 * Shotguns are, in general, not as heavily regulated by legislation as handguns are (and are thus easier to obtain).
 * When loaded with smaller shot, a shotgun will not penetrate walls as readily as rifle and pistol rounds, making it safer for non-combatants when fired in or around populated structures.

Military
Shotguns are common weapons in military use, particularly for special purposes. Shotguns are found aboard Naval vessels for shipboard security and are used by military police units. United States Marines have used shotguns since their inception at the squad level, often in the hands of NCOs, while the US Army often issued them to a squad's point man. Shotguns were modified for and used in the trench warfare of WWI, in the jungle combat of WWII and Vietnam and are being used today in Iraq, being popular with soldiers and Marines in urban combat environments.

Definition
The wide range of forms the shotgun can take leads to some significant differences between what is technically a shotgun and what is legally considered a shotgun. A fairly broad attempt to define a shotgun is made in the United States legal code (18 USC 921), which defines the shotgun as "a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder, and designed or redesigned and made or remade to use the energy of the explosive in a fixed shotgun shell to fire through a smooth bore either a number of ball shot or a single projectile for each single pull of the trigger."

A rifled slug, with finned rifling designed to spin the bullet and stabilize it in order to improve its accuracy, is an example of a single projectile. Some shotguns have rifled barrels and are designed to be used with a "saboted" bullet, one which is typically encased in a two-piece plastic ring (sabot) designed to peel away after it exits the barrel, leaving the bullet, now spinning after passing through the rifled barrel, to continue toward the target. These shotguns, although they have rifled barrels, still use a shotgun-style shell instead of a rifle cartridge and may in fact still fire regular multipellet shotgun shells, but the rifling in the barrel will affect the shot pattern. The use of a rifled barrel blurs the distinction between rifle and shotgun, and in fact the early rifled shotgun barrels went by the name Paradox for just that reason. Hunting laws may differentiate between smooth barreled and rifled barreled guns.

Also, many people would likely call a fully automatic shotgun a shotgun, even though legally it would fall into a different category. Amongst the general populace, any gun that fires shotgun shells could be considered a shotgun. This might include the rare shot-pistol (a pistol designed to fire a standard shotgun shell).

Riot gun has long been a synonym for a shotgun, especially a short-barrelled shotgun. During the 19th and early 20th century, these were used to disperse rioters and revolutionaries. The wide spray of the shot ensured a large group would be hit, but the light shot would ensure more wounds than fatalities. When the ground was paved, police officers would often ricochet the shot off the ground, slowing down the shot and spreading pattern even further. To this day specialized police and defensive shotguns are called riot shotguns. The introduction of rubber bullets and bean bag rounds ended the practice of using shot for the most part, but riot shotguns are still used to fire a variety of less than lethal rounds for riot control.

A sawed-off shotgun refers to a shotgun whose barrel has been shortened, leaving it more maneuverable, easier to use at short range and more readily concealed. Because of the traditionally nefarious uses for such weapons, many countries establish a legal minimum barrel length. The sawed-off shotgun is sometimes known as a "Lupara" (in Italian a generic reference to the word "Lupo" ("Wolf")) in Southern Italy and Sicily.

Coach guns are similar to sawn-off shotguns, except they are manufactured with an 46 cm (18") barrel and are legal for civilian ownership in some jurisdictions. Coach guns are also more commonly associated with the American Old West or Australian Colonial period, and often used for hunting in bush, scrub, or marshland where a longer barrel would be unwieldy or impractical.

A backpacker shotgun has a short barrel and either a full-size stock or pistol grip, depending on legislation in intended markets. The overall length of these weapons is frequently less than 90 cm (36 inches), with some measuring up at less than 63 cm (25 inches). These weapons are typically break-action .410 "gauge" (caliber), single-barrel designs with no magazine and no automatic ejection capability. They typically employ a cylinder bore, but infrequently are available in modified choke as well. One example of a backpacker shotgun is the Verney-Carron Snake Charmer or the pistol grip Snake Charmer II. Backpacker shotguns are popular for "home defense" purposes and as "survival" weapons. Other examples include a variety of .410 / rifle "survival" guns manufactured in over/under designs. In the drilling arrangement, a rimfire or centrefire rifle barrel is located beneath the barrel of a .410 gauge shotgun. Generally, there is one manually-cocked external hammer and an external selection lever to select which caliber of cartridge to fire. A notable example is the Springfield Arms M6 Scout, a .410 / .22 backpacker drilling issued to United States Air Force personnel as a "survival" gun in the event of a forced landing or accident in a wilderness area. Variants have been used by Israeli, Canadian, and American armed forces. Shotgun/rifle combination guns with two, three, and occasionally even four barrels are available from a number of makers, primarily European. These provided flexibility, enabling the hunter to effectively shoot at flushing birds or more distant small mammals while only carrying one gun.

History
Since early firearms, such as the blunderbuss, arquebus and musket tended to have large diameter, smoothbore barrels, they would function with shot as well as solid balls. A firearm intended for use in wing shooting of birds was known as a fowling piece. The 1728  Cyclopaedia defines a fowling piece as:


 * Fowling Piece, a portable Fire Arm for the shooting of Birds. See Fire Arm.
 * Of Fowling Pieces, those are reputed the best, which have the longest Barrel, vis. from 5 1/2 foot to 6; with an indifferent Bore, under Harquebus: Tho' for different Occasions they shou'd be of different Sorts, and Sizes.  But in all, 'tis essential the Barrel be well polish'd and smooth within; and the Bore all of a Bigness, from one End to another...

For example, the contemporary Brown Bess musket, in service with the British military from 1722 to 1838, 19 mm (.75 inch) smoothbore barrel, roughly the same as a 10 gauge shotgun, and was 157 cm (62 inches) long, just short of the above recommended 168 cm (5 1/2 feet). On the other hand, records from the Plymouth colony show a maximum length of 137 cm (4 1/2 feet) for fowling pieces, shorter than the typical musket.

Shot was also used in warfare; the buck and ball loading, mixing a musket ball with three or six buckshot, was used throughout the history of the smoothbore musket. The first recorded use of the term shotgun was in 1776 in Kentucky. It was noted as part of the "frontier language of the West" by James Fenimore Cooper.

With the adoption of the smaller bores and rifled barrels, the shotgun began to emerge as a separate entity. Shotguns have long been the preferred method for sport hunting of birds, and the largest shotguns, the punt guns, were used for commercial hunting. The double-barreled shotgun, for example, has changed little since the development of the boxlock action in 1875. Modern innovations such as interchangeable chokes and subgauge inserts make the double barreled shotgun the shotgun of choice in skeet, trap shooting, and sporting clays, as well as with many hunters. A double from a well respected maker, such as Kreighoff or Perazzi, can cost US$5,000 to start, and reach prices of US$100,000 for presentation grade examples. Far less expensive is the pump action shotgun, such as the Mossberg 500, Remington 870 or Winchester 1300, many models of which retail for under US$350.

During its long history, it has been favored by bird hunters, guards and law enforcement officials. The shotgun has fallen in and out of favor with military forces several times in its long history. Shotguns and similar weapons are simpler than long-range rifles, and were developed earlier. The development of more accurate and deadlier long-range rifles minimized the usefulness of the shotgun on the open battlefields of European wars. But armies have "rediscovered" the shotgun for specialty uses many times.

19th century
During the 1800s, shotguns were mainly employed by cavalry units. Cavalry units on both sides of the American Civil War employed shotguns. American cavalry went on to use the shotgun extensively during the Indian Wars throughout the latter half of the 19th century. Horseback units favored the shotgun for its moving target effectiveness, and devastating close-range firepower. The shotgun was also favored by citizen militias and similar groups. The shotgun was used in the defense of The Alamo during Texas' War of Independence with Mexico.

With the exception of cavalry units, the shotgun saw less and less use throughout the 19th century on the battlefield. As a defense weapon it remained popular with guards and lawmen, however, and the shotgun became one of many symbols of the American Old West. The famous lawman Cody Lyons killed two men with a shotgun; his friend Doc Holliday's only confirmed kill was with a shotgun. The weapon both these men used was the short-barreled version favored by private strongbox guards on stages and trains. These guards, called express messengers became known as shotgun messengers, since they rode with the weapon (loaded with buckshot) for defense against bandits. Passenger carriages carrying a strongbox usually had at least one private guard armed with a shotgun riding in front of the coach, next to the driver. This practice has survived in American slang; the term "riding shotgun" is used for the passenger who sits in the front passenger seat. The shotgun was a popular weapon for personal protection in the American Old West, requiring less skill on the part of the user than a revolver.

Daniel Myron LeFever
Daniel Myron LeFever is credited with the invention of the hammerless shotgun. Working for Barber & LeFever in Syracuse, N.Y. he introduced the first hammerless shotgun in 1878. This gun was cocked with external cocking levers on the side of the breech. He formed his own company, The LeFever Arms Co., in 1880 and went on to patent the first truly automatic hammerless shotgun in 1883. This gun automatically cocked itself when the breech was closed. He later developed the mechanism to automatically eject the shells when the breech was opened. The LeFever Arms Co. went on to make some of the finest double barrel shotguns in America until they were bought by The Ithaca Gun Co. in 1916.

John Moses Browning
One of the men most responsible for the modern development of the shotgun was prolific gun designer John Browning. While working for Winchester Firearms, Browning revolutionized shotgun design. In 1887, Browning introduced the Model 1887 Lever Action Repeating Shotgun, which loaded a fresh cartridge from its internal magazine by the operation of the action lever. Before this time most shotguns were the 'break open' type.

This development was greatly overshadowed by two further innovations he introduced at the end of the 19th century. In 1893, Browning produced the Model 1893 Pump Action Shotgun, introducing the now familiar pump action to the market. And in 1900, he patented the Browning Auto-5, the world's first semi-automatic shotgun. The Browning Auto-5 remained in production until 1998.

World wars
The decline in military use of shotguns reversed in World War I. American forces under General Pershing employed 12-gauge pump action shotguns when they were deployed to the Western front in 1917. These shotguns were fitted with bayonets and a heat shield so the barrel could be gripped while the bayonet was deployed. Shotguns fitted in this fashion became known as trench guns by the United States Army. Those without such modifications were known as riot guns. After World War I, the United States military began referring to all shotguns as riot guns.

Due to the cramped conditions of trench warfare, the American shotguns were extremely effective. Germany even filed an official diplomatic protest against their use, alleging they violated the laws of warfare. The Judge Advocate General reviewed the protest, and it was rejected because the Germans protested use of lead shot (which would have been illegal) but military shot was plated. This is the only occasion the legality of the shotgun's use in warfare has been questioned.



During World War II, the shotgun was not heavily used in the war in Europe by official military forces. However, the shotgun was a favorite weapon of Allied-supported partisans, such as the French Resistance. By contrast, in the Pacific theater, thick jungles and heavily-fortified positions made the shotgun a favorite weapon of the United States Marines. Marines tended to use pump shotguns, since the pump action was less likely to jam in the humid and dirty conditions of the Pacific campaign. Similarly, the United States Navy used pump shotguns as well to guard ships when in port in Chinese harbors (e.g., Shanghai). The United States Army Air Forces similarly used pump shotguns to guard bombers and other aircraft against saboteurs when parked on airbases across the Pacific and on the West Coast of the United States. Pump and semi-automatic shotguns were used in marksmanship training, particularly for bomber gunners. The most common pump shotguns used for these duties were the 12 gauge Winchester Model 97 and Model 12.

Late 20th century to present
Since the end of World War II, the shotgun has remained a specialty weapon for modern armies. It has been deployed for specialized tasks where its strengths were put to particularly good use. It was used to defend machine gun emplacements during the Korean War, American and French jungle patrols used shotguns during the Vietnam War, and shotguns saw extensive use as door breaching and close quarter weapons in the early stages of the Iraq War, and saw limited use in tank crews. Many modern navies make extensive use of shotguns by personnel engaged in boarding hostile ships, as any shots fired will almost certainly be over a short range. Shotguns are far from being as common amongst military forces as rifles, carbines, or submachineguns.

On the other hand, the shotgun has become a standard in law enforcement use. A variety of specialty less-lethal or non-lethal ammunitions, such as tear gas shells, bean bags, flares, explosive sonic stun rounds, and rubber projectiles, all packaged into 12 gauge shotgun shells, are produced specifically for the law enforcement market. Recently TASER international introduced a self-contained electronic weapon which is fired from a standard 12 gauge shotgun.

The shotgun remains a standard firearm for hunting throughout the world for all sorts of game from birds and small game to large game such as deer. The versatility of the shotgun as a hunting weapon has steadily increased as slug rounds and more advanced rifled barrels have given shotguns longer range and killing power. The shotgun has become a ubiquitous firearm in the hunting community. The prevalence of the shotgun's use in hunting can be easily shown by the number of hunting incidents reported to wildlife and game officials. Of the thirty-four hunting accidents reported in Wisconsin in 2005, sixteen involved shotguns, making them the most common hunting firearm. The second most common was rifles of various calibers. (Wisconsin Department of Natural Resources, 2005 )

In 1994, shotguns made up 9.7% of gun traces relating to criminal investigations in the United States and were the weapon of choice in 5% of homicides according to United States Justice Department statistics. Shotguns are not the preferred weapons for criminal activity, since criminals prefer weapons which are more easily concealed, according to the National Crime Victimization Survey. However, the comparatively easy availability of double-barrelled shotguns compared to pistols in the United Kingdom and Australia, coupled with the ease with which their barrels and stocks can be shortened, has made the sawn-off shotgun a popular weapon of armed robbers in these countries.

Action
Action is the term for the operating mechanism of a gun. There are many types of shotguns, typically categorized by the number of barrels or the way the gun is reloaded.

Break-action
For most of the history of the shotgun, the breech loading double barreled shotgun was the most common type, typically divided into two subtypes: the traditional "side by side" shotgun features two barrels mounted one beside the other (as the name suggests), whereas the "over and under" shotgun has the two barrels mounted 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 birds), whereas over and under shotguns are more commonly associated with sporting use (such as clay pigeon/skeet shooting). Having said that, 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 shotgun barrel and one rifle barrel (more often rifle on top, but rifle on bottom was not uncommon). There is also a class of break action guns called drillings, which contain three barrels, usually 2 shotgun barrels of the same gauge and a rifle barrel, though the only common theme is that at least one barrel be a shotgun barrel. The most common arrangement was essentially a side by side shotgun with the rifle barrel below and centered. Usually a drilling containing more than one rifle barrel would have both rifle 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
In pump-action shotguns (also known as Riot Guns), a sliding forearm handle (the pump) works the action, extracting the spent shell and inserting a new one as the pump is worked. A pump gun is typically fed from a tubular magazine underneath the barrel, which also serves as a guide for the pump. The rounds are fed in one by one through a port in the receiver, where they are pushed forward. A latch at the rear of the magazine holds the rounds in place in the magazine until they are needed. 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 with shorter barrels and no barrel choke (or very little) are highly popular for use in home defense and law enforcement applications. The minimum barrel length for shotguns in most of the U.S. is 18", as opposed to 24-28" commonly used for hunting. This 18" barrel (sometimes 18.5" to ensure differences in manufacturing or measuring do not make the gun illegal) is the primary choice for pump-action shotguns used for defense as the shorter barrel makes the weapon easier to maneuver around corners and in tight spaces, though longer barrels are sometimes used for a tighter spread pattern or increased accuracy of slug projectiles. Home-defense/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 allowing easier use by novice shooters.

A shorter barreled shotgun has many advantages over a handgun or rifle. Compared to a handguns chambered for 9mm Parabellum, .38 Special, .357 Magnum, .40 S&W, .45ACP and similar, a shotgun has far more power and damage potential, allowing a "one-shot stop" that is more difficult to achieve with typical handgun loads. Compared to a rifle, most shorter barreled shotguns are easier to maneuver, and still provide better damage potential at indoor distances (generally 3-5 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 increases the effectiveness of "point shooting" - rapidly aiming simply by pointing the weapon in the direction of the target, allowing easy, fast use by novices.

Lever-action
Early attempts at repeating shotguns invariably centred around either bolt-action or lever-action designs- drawing inspiration from contemporary repeating rifle designs- with the earliest successful repeating shotgun being the lever-action Winchester M1887, designed by John Browning in 1887 at the behest of the Winchester Repeating Arms Company. Lever-action shotguns, while less common, were popular in the late 1800s with the Winchester Model 1887 and Model 1901 being prime examples. Initially very popular, demand waned after the introduction of pump-action shotguns at the turn of the 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 shells are made of 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 shotshells.

Semi-automatic
Gas, inertia, or recoil operated actions are other popular methods of increasing the rate of fire of a shotgun; these are generally referred to as autoloaders or semi-automatics. 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. Well-known examples include the Remington 1100, Browning A-5, Benelli M1, and Saiga-12 series shotguns.

Some, such as the Franchi SPAS-12, and the Benelli M3, are capable of switching between semi-automatic and pump action.

Bolt-action
Bolt-action shotguns, while rather 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 Ishapore Arsenal in India also manufactured a single-shot .410 gauge shotgun based on the SMLE Mk III* rifle. The Russian Berdana shotgun was effectively a one-round bolt-action rifle that became obsolete, and was subsequently modified to chamber 16 gauge shotgun shells for civilian sale.

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 Auto-Assault 12 (See Atchisson Assault Shotgun). These combat shotguns, while popular in movies and computer games due to their exotic nature, have yet to make a noticeable impression in the real world.

Gauge


The caliber of shotguns is measured in terms of gauge (U.S.) or bore (U.K.). The gauge number is determined by the number of solid spheres of a diameter equal to the inside diameter of the barrel that could be made from a pound of lead. 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. By far the most common gauges are 12 (0.729 in, 18.5mm diameter) and 20 (15.6 mm, 0.614 in), although .410 (= 36), 32, 28, 24, 16, and 10 (19.7 mm) gauge and 9mm (.355 in.) and .22 (5.5mm) rimfire calibres have also been produced (although 10, 12, 16, 20, 28, .410, and .22 are the only legal hunting gauges/calibers in most U.S. states). To further complicate matters, typical handgun chamberings such as 9 mm Parabellum, .45 ACP, .38 Special/.357 Magnum, .44 Special/.44 Magnum, and .45 Colt and others bearing a "shot" load have been brought to market by CCI/Speer--either crimped in or in a plastic casing replacing the bullet. These are not generally considered "shot shells" by shotgun users, and the patterning performance is questionable since they are fired through rifled barrels. Thompson/Center makes special pistol barrels in .38/.357, .44 and .45 Colt that have "straight rifled" chokes in them to reduce the spin of the shot column and produce better patterns, but they are still suitable only for pest control at very short ranges. Larger gauges, too powerful to shoulder, have been built but were generally affixed to small boats and referred to as punt guns. These were used for commercial water fowl hunting, to kill large numbers of birds resting on the water. Although relatively rare, single and double derringers 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', and are popular among some outdoorsmen in the South and Southwest regions of the United States. There are also some revolvers, such as the Taurus Judge, that are capable of shooting the .45LC/.410 rounds; but as with derringers, these are handguns that shoot .410 shotgun shells, and are not necessarily considered shotguns themselves.

The .410 bore (10.4mm) 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 beginners 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 quails and doves. 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 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 very suitable gauge for many popular hunting uses.

A recent innovation is the back-boring of barrels, in which the barrels themselves 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
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 5 mm (0.20 inches) and buckshot are larger than that. Pellet size is indicated by a number, for bird shot this ranges from the smallest 12 (1.2 mm, 0.05 in) to 2 (3.8 mm, 0.15 in) and then BB (4.6 mm, 0.18 in). For buckshot the numbers usually start at 4 (6.1 mm, 0.24 in) and go down to 1, 0, 00, 000, and finally 0000 (9.7 mm, .38 in). A different informal distinction is that "bird shot" pellets are small enough that they can be measured into the cartridge by weight, and just poured in, whereas "buckshot" pellets are so large they won't all fit unless they're stacked inside the cartridge one by one in a certain particular geometric arrangement. The diameter in hundreths of an inch of bird shot sizes from #9 to #1 can be obtained by subtracting the shot size from 17. Thus, #4 bird shot is 17 - 4 = 13 = 0.13 inches (3.3 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 "S.G." (small game) cartridges.

Pattern and choke
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. 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 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 30 inch (76cm) 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&mdash;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 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 top maker of interchangeable shotgun chokes, uses a conical portion about 3 times the bore diameter in length, so 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). There is no good mathematical model that describes how chokes work, making the design and manufacture for chokes more art than science. 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 0.005 inches (127 micrometres) of constriction to produce a 76 cm (30 inch) diameter pattern at a distance of 19 m (21 yards). A trap shooter, shooting at distant targets might use 762 micrometres (0.030 inches) of constriction to produce a 76 cm (30 inch) diameter pattern at 37 m (40 yards). 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 inches). 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

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 cm twist, as does the FABARM Lion Paradox shotgun.

Oval chokes 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. 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.

Barrel length
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 25 to 36 cm 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. On uphill shooting, this means to shoot above the target. Conversely, on downhill shooting, this means to shoot below the target, which is somewhat counterintuitive for many beginning hunters. Of course, depending on the barrel length, the amount of lead employed will vary for different barrel lengths, and must be learned by experience.

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 24 to 28 inches (610 to 710 mm). Shotguns for longer range shooting, where angular speeds are less (trap shooting; quail, pheasant, and waterfowl hunting) tend to have longer barrels, 28 to 34 inches. The longer barrels have more inertia, and will therefore swing more slowly but more steadily. The short, low inertia 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 9 and 15 cm (3.5 and 6 inches) in overall length, but in most cases pays for this by having two barrels, which adds weight at the muzzle, and so usually only adds a couple of centimetres. 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 56 to 61 cm (22 to 24 inches).

Shotguns intended for all-round hunting are a compromise, of course, but a 72 to 74 cm (28-29 inch) 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.

Ammunition


The extremely large caliber of shotgun shells has led to a wide variety of different ammunition. Standard types include:


 * Shot  (also known as birdshot in the smaller shot sizes) is the most commonly used round, filled with lead or lead substitute pellets. Shot shells are described by the size of the pellets within, and numbered in reverse order (ie; the bigger the shot, the smaller the number). Size nine (#9) shot is the smallest size normally used for hunting and is used on small upland game birds such as dove and quail. Larger sizes are used for hunting larger upland game birds and waterfowl. In Europe and in other countries that use the metric system of measurement, except Canada, the shot size is simply the diameter of the pellet given in millimeters.
 * Buckshot, is larger than birdshot, and was originally designed for hunting larger game, such as deer. While the advent of new, more accurate slug technologies is making buckshot less attractive for hunting, it is still the most common choice for police, military, and home defense uses. Like birdshot, buckshot is described by pellet size, with larger numbers indicating smaller shot. From the smallest to the largest, buckshot sizes are: #4, (called "number four"), #1, 0 ("one-aught"), 00 ("double-aught"), 000 ("triple-aught") and 0000 ("four-aught"). A common round for defensive use would be a 12 gauge 7 cm (2 3/4") length 00 buck shell, which contains 9 balls of roughly 8.4 (.33 inch) caliber. New "tactical" buckshot rounds, designed specifically for defensive use, use slightly fewer shot at lower velocity to reduce recoil and increase controllability of the shotgun.
 * Slug rounds are rounds that fire a single solid slug. They are used for hunting large game, and in certain military and law enforcement applications. Modern slugs are moderately accurate, especially when fired from special rifled slug barrels. They are often used in "shotgun-only" hunting zones near inhabited areas, where rifles are prohibited due to their excessive range.

Specialty ammunition
The unique properties of the shotgun, such as large case capacity, large bore, and the lack of rifling, has led to the development of a large variety of specialty shells, ranging from novelties to high tech military rounds.


 * Hunting, defensive, and military
 * Brenneke and Foster type slugs have the same basic configuration as normal slugs, but have increased accuracy. The hollowed rear of the Foster slug improves accuracy by placing more mass in the front of the projectile, therefore inhibiting the "tumble" that normal slugs may generate. The Brenneke slug takes this concept a bit further, with the addition of a wad that stays connected to the projectile after discharge, increasing accuracy. Both slugs are commonly found with fins or rib, which are meant to allow the projectile to safely squeeze down during passage through chokes, but they do not increase stability in flight.
 * Flechette rounds contain aerodynamic darts, typically from 8 to 20 in number. The flechette provide greatly extended range due to their aerodynamic shape, and improved penetration of light armor. American troops during the Vietnam War packed their own flechette shotgun rounds, called beehive rounds, after the similar artillery rounds. However, terminal performance was poor due to the very light weight of the flechettes, and their use was quickly dropped.
 * Frag-12 shotgun round is a series of special purpose shotgun grenades, including high explosive blast, fragmentation, and HEAP grenades intended to be fired from any 12-ga shotgun. It has been proposed as an armament for modern UAVs and is currently being tested for military deployment.
 * Grenade rounds use exploding projectiles to increase long range lethality. These are currently experimental, but the British FRAG-12, which comes in both armor penetrating and fragmentary forms, is under consideration by military forces


 * Less-than-lethal rounds, for riot and animal control
 * Flexible baton rounds, commonly called bean bags, fire a fabric bag filled with birdshot or a similar loose, dense substance. The 'punch' effect of the bag is useful for knocking down targets and are used by police to subdue violent suspects. The bean bag round is by far the most common less lethal round used. Due to the large surface area of these rounds, they lose velocity rapidly, and must be used at fairly short ranges to be effective, though use an extremely short ranges, under 3 m (10 feet) their use can result in broken bones or other serious or lethal injury.
 * Gas shells spray a cone of gas for several meters. These are primarily used by riot police. They normally contain pepper gas or tear gas. Other variations launch a gas grenade-like projectile.
 * Rock salt shells are hand loaded with rock salt, replacing the standard shot. Rock salt shells were used by rural civilians to defend their property, and were the forerunners of modern less-than-lethal rounds. The brittle salt was unlikely to cause serious injury at long ranges, but would cause light stinging injuries. The use of this ammunition is mainly anecdotal, though there was a documented case in 2004.
 * Rubber slugs or rubber buckshot are similar in principle to the bean bag rounds. Composed of flexible rubber or plastic and fired at low velocities, these rounds are probably the most common choice for riot control. Shapes range from full bore diameter cylinders to round balls of varying sizes, to a patent pending design "star round" that resembles a small koosh ball.
 * TASER International announced in 2007 a new 12 gauge eXtended Range Electronic Projectile or XREP, which contains a small electroshock weapon unit in a carrier that can be fired from a standard 12 gauge shotgun. The XREP projectile is fin stabilized, and travels at an initial velocity of 100 m/s (300 fps).  Barbs on the front attach the electroshock unit to the target, with a tassel deploying from the rear to widen the circuit. A twenty second burst of electrical energy is delivered to the target.  This product is expected to be released to market in 2008
 * Breaching rounds, often called Disintegrator or Hatton rounds, are designed to blow out deadbolts, door locks and door hinges without risking the lives of those beyond the door. These frangible rounds made of a dense sintered material, often metal powder in a binder such as wax, which can destroy a lock then immediately disperse. They are used by military and SWAT teams to quickly force entry into a locked room. Amongst police, these rounds are nicknamed 'master keys', and their use is known as 'Avon calling'.
 * Bird bombs are low-powered rounds that fire a firecracker that is fused to explode a short time after firing . They are designed to scare animals, such as birds that congregate on airport runways.
 * Screechers fire a pyrotechnic whistle that emits a loud whistling sound for the duration of its flight . These are also used to scare animals.
 * Blank shells contain only a small amount of powder and no actual load. When fired, the blanks provide the sound and flash of a real load, but with no projectile . These may be used for simulation of gunfire, scaring wildlife, or as power for a launching device.
 * Stinger is a type of shotgun shell which contains 16-00 buck balls made of zytel, and is designed as a non-lethal ammunition ideally used in small spaces.


 * Novelty and other
 * Bolo rounds contain two round balls connected with wire or two flat pieces connected with wire.
 * Dragon's Breath usually refers to a zirconium-based pyrotechnic shotgun round. When fired, a gout of flame erupts from the barrel of the gun (up to 20 ft). While it has no tactical uses, the visual effect it produces is impressive, similar to that of a short ranged flamethrower.
 * Flare rounds are sometimes carried by hunters for safety and rescue purposes. They are available in low and high altitude versions. Some brands claim they can reach a height of up to 200 m (600 feet).

Legal issues
Globally, shotguns are generally not as heavily regulated as rifles or handguns, likely because they lack the range of rifles, yet are not easily concealable as handguns are; thus, they are perceived as a lesser threat by legislative authorities. The one exception is a sawn-off shotgun, especially a Lupara, as it is as highly concealable as a handgun and has had a long history associated with crime.

UK
In the United Kingdom, a Shotgun Certificate (SGC) is required to possess a shotgun. These cost £50 and can only be denied if the chief of police in the area believes and can prove that the applicant poses a real danger to the public, or if the applicant has been convicted of a crime punishable by imprisonment for a term of three years or more (unless they have been acquitted) or if the applicant cannot securely store a shotgun (gun clamps, wire locks and locking gun cabinets are considered secure). The round number restrictions apply only to the magazine, not the chamber, so it is legal to have a single-barreled semi-auto or pump-action shotgun that holds three rounds in total, or a shotgun with 5 separate chambers that holds 5 rounds. However, revolver guns do not fall into this category so multi-chamber shotguns would need to also be multi-barrel. For a shotgun to be held on an SGC,it must be a smooth-bore gun (that is not an air-gun) which:

(a) has a barrel not less than 24 inces in length and does not have any barrel with a bore more than 2 inches in diameter;

(b) either has no magazine or has a non-detachable magazine not capable of holding more than two cartridges;

(c) is not a revolver gun.

Prior to a SGC being issued an interview is conducted with the local Firearms Officer, in the past this was a duty undertaken by the local police although more recently this function has been "contracted out" to civilian staff. The officer will check the location and suitablity of the gun safe that is to be used for storage and conduct a general interview to establish the reasons behind the applicant requiring a SGC.

An SGC holder can own any number of shotguns meeting these requirements so long as he can store them securely. No certificate is required to own shotgun ammunition, but one is required to buy it. There is no restriction on the amount of shotgun ammunition that can be bought or owned. There are also no rules regarding the storage of ammunition.

However, shotgun ammunition which contains fewer than 6 projectiles requires the appropriate Firearms Certificate (FAC). Shotguns with a magazine capacity greater than 2 rounds also require the appropriate Firearms Certificate to own. An FAC costs £50 but is much more restrictive than an SGC. A new 'variation' is required for each new caliber of gun to be owned, limits are set on how much ammunition a person can own at any one time, and an FAC can be denied if the applicant does not have sufficient 'good reason'. 'Good reason' generally means hunting, collecting or target shooting - though other reasons may be acceptable.

USA
In the United States, federal law prohibits shotguns from being capable of holding more than three shells including the round in the chamber when used for hunting migratory waterfowl such as ducks and geese. For other uses, a capacity of any number of shells is generally permitted. Most magazine-fed shotguns come with a removable magazine plug to limit capacity to 2, plus one in the chamber, for hunting migratory waterfowl. Certain states have restrictions on magazine capacity or design features under hunting or assault weapon laws.

Shotguns intended for defensive use are as short as 46 cm (18 inches) for private use (the minimum shotgun barrel length allowed by law in the United States without special permits). Barrel lengths of less than 46 cm (18 inches) as measured from the breechface to the muzzle when the weapon is in battery with its action closed and ready to fire, or have an overall length of less than 66 cm (26 inches) are classified as short barreled shotguns (AKA "sawn-off shotguns") under the 1934 National Firearms Act and are heavily regulated.

Shotguns used by military, police, and other government agencies are exempted from regulation under the National Firearms Act of 1934, and often have barrels as short as 30 to 36 cm (12 to 14 inches), so that they are easier to handle in confined spaces. Non-prohibited private citizens may own short-barreled shotguns by purchasing a $200 tax stamp from the Federal government and passing an extensive background check (state and local laws may be more restrictive). Defensive shotguns sometimes have no buttstock or will have a folding stock to reduce overall length even more when required.

According to US law, a shotgun can be any weapon which fires a shotgun shell. This is because the first shotgun was little more than a pipe and a smaller tube filled with lead balls with gunpower mixed in.

Australia
Within Australia, all shotguns manufactured after January 1, 1901 are considered firearms and are subject to registration and licensing. Most shotguns (including break-action, bolt-action and lever-action shotguns) are classed as "Category A" weapons and, as such, are comparatively easy to obtain a licence for, given a legally-recognised 'legitimate reason' (compare to the British requirement for 'good reason' for a FAC), such as target shooting or hunting. However, pump-action and semi-automatic shotguns are classed as "Category C" weapons; a licence for this type of firearm is, generally speaking, not available to the average citizen. For more information, see Gun politics in Australia.