This article is about the firearm. For alternative meanings of shotgun, see: Shotgun (disambiguation).

A shotgun is a firearm typically used to fire a number of small balls, the shot, from a smoothbore barrel of relatively large diameter. The energy of any one ball of shot is fairly low, making shotguns useful primarily for hunting birds and other small game, or as close-combat weapons or defensive weapons where the short range ensures that many of the balls of shot will hit the target (see riot shotgun and combat shotgun).

The shotgun has several advantages over a normal gun. It has enormous stopping power at short range. The wide spread of shot produced by the gun makes it easy to aim and to be used by inexperienced marksmen. Also, shot is less likely to penetrate walls and hit bystanders. It is favored by law enforcement for its low penetration and high stopping power, while many American households use it as a home defense weapon for its ease of use and wide spray.

Contents

1 Definition 2 History and etymology 3 Design factors 3.1 Action 3.2 Gauge 3.3 Shot 3.4 Choke and pattern 3.5 Barrel length 4 Common uses 5 Ammunition 5.1 Specialty ammunition 6 References

Definition

The United States legal code (18 USC 921) 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." United Kingdom law requires that a shotgun not be capable of holding more than three rounds; if it holds more it is classed as a firearm. In the United States, shotguns which have barrel lengths of less than 18 inches (457 mm) 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 26 inches (660 mm) are classified as short barreled shotguns (AKA "sawn-off shotguns") under the National Firearms Act of 1934 and heavily regulated.

This definition, however, does not exactly match the technical use of the term, which would include the growing number of shotguns specifically designed to fire single projectiles instead of shot. 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. A saboted bullet is typically encased in two-piece plastic ring (sabot) which is designed to fall away after it passes the end of 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. Hunting laws may differentiate between smooth barreled and rifled barreled guns.

Also, technically speaking, many people would likely call a fully automatic shotgun a shotgun, even though legally it would fall under a different category.

History and etymology

Shotguns have also been referred to as "scatterguns", "fowling pieces" or "two-shoot guns" historically, and were used as a replacement for the blunderbuss. 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. During its long history, it has been favored by bird hunters, guards and law enforcement officials.

Design factors

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. For most of the history of the shotgun, the double barreled shotgun, with two barrels, was the most common type. In this case there are several "subtypes", the over and under shotgun puts the two barrels one on top of the other, while the side-by-side shotgun puts them beside each other. In pump-action shotguns, a sliding forearm handle, the pump, works the action to reload the single barrel. Gas, inertia, or recoil operated actions are other popular methods of increasing the rate of fire of a shotgun; these actions are generally referred to as autoloaders or semi-automatic shotguns. A small number of guns are available with a bolt action, but this is uncommon. Some shotguns, such as the Franchi SPAS-12 and Benelli M3, are capable of switching between semi-automatic and pump action.

Some of the more interesting advances in shotgun technology include the versatile NeoStead 2000 and fully automatics such as the Pancor Jackhammer. 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 or bore (the British English term). 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 has 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 (0.73 in, 18.5 mm diameter) and 20 (0.614 in, 15.6 mm), although 4, 8, 10, 14, 16, 24, 28, 32 gauges and the .410 calibre (10 mm) have also been produced. 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 water fowl hunting, to kill large numbers of birds resting on the water.

The .410 calibre (10 mm) is measured in inches instead of gauge for historical reasons. The .410 calibre (10 mm), approximately 67 gauge, was created to impose maximum handicap upon skilled shooters in the game of skeet, by throwing a relatively small charge of shot. The .410 calibre (10 mm) was not created for hunting, but some people do use it for that.

Shot

Despite the above mention of slugs and sabots most shotguns are used to fire "a number of ball shot". 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 0.20 inches (5 mm) and buckshot larger. Pellet size is indicated by a number, for birdshot this ranges from the smallest 12 (0.05 in) to 2 (0.15 in) and then BB (0.18 in), for buckshot the numbers usually start at 4 (0.24 in) and go down to 1, 0, 00 and finally 000 (0.36 in). A different informal distinction is that "birdshot" pellets are small enough that they can be measured into the cartridge by weight, and just poured in, whereas "buckshot" pellets are so large that they won't all fit unless they're stacked inside the cartridge one by one in a certain particular geometric arrangement; by this definition, #4 buckshot, 0.24 in in diameter (6.3 mm) is buckshot because the pellets have to be stacked in a certain arrangement inside the cartridge or else they won't all fit, but anything smaller can be measured by weight and just dumped in. The diameter in hundredths of inches of shot sizes from #9 to #2 can be obtained by subtracting the shot size from 17. Thus, #4 shot is 17 - 4 = 13 = 0.13 inches (3.3 mm) in diameter.

Choke and pattern

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. A constriction in the end of the barrel known as the choke is used to tailor the pattern for different purposes. A skeet shooter, shooting at close targets might use 0.005 inches (127 micrometres) of constriction to produce a 30 inch (762 mm) diameter pattern at a distance of 21 yards (19 m). A trap shooter, shooting at distant targets might use 0.030 inches (762 micrometres) of constriction to produce a 30 inch (762 mm) diameter pattern at 40 yards (37 m). 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

Table of shotgun chokes
for a 12 gauge shotgun using lead shot

Constriction (inches)	Constriction (micrometres)	American Name	percentage of shot in a 30 in (762 mm) circle at 40 yd (37 m)	Effective range (yd)	Effective range (m)
0.000	0	Cylinder	40	20	18
0.005	127	Skeet	45	23	21
0.010	254	Improved Cylinder	50	25	23
0.015	381	Light Modified
0.020	508	Modified	60	35	32
0.025	635	Improved Modified
0.030	762	Light Full
0.035	889	Full	70	40	37
0.045	1143	Extra Full
0.050	1270	Super Full

Barrel length

Shotguns generally have longer barrels than 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. 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 shooting, or inland 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 and waterfowl hunting) tend to have longer barrels, 28 to 34 inches. The longer barrels have more inertia, and will therefore swing slower but steadier. 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 3.5 and 6 inches (90 and 150 mm) 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 inches (50 mm). 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 game like rabbits and squirrels, or shotguns for use with buckshot for deer, are usually 22 to 24 inches (560 to 610 mm). Shotgun intended for defensive use are as short as 18 inches (457 mm) for civilian use (the minimum barrel length allowed by law in the United States). Military and police shotguns, which are not regulated by law, often have barrels as short as 12 to 14 inches (305 to 356 mm), so that they are easier to handle in confined spaces. Defensive shotguns will often have no buttstock or a folding stock to reduce overall length even more.

Common uses

In hunting circles, the shotgun is used for bird hunting, although it is also increasingly used in deer hunting in semi-populated areas where the long-distance travel of the rifle bullet may pose too great a hazard. Many modern smooth bore shotguns using rifled slugs are extremely accurate out to 75 yards (69 m) or more, while the rifled barrel shotgun with the use of sabot slugs are typically accurate to 100 yards (91 m) 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 1,500 feet per second (450 m/s) and blunt, poorly streamlined shape of typical slugs (which cause them to lose velocity very rapidly, compared to rifle bullets), even a very skilled marksman will find it difficult to make a humane killing shot on a deer much past 110 yards (100 m) due to the rapid drop of a slug's trajectory past that point; with slugs, at 150 meters the marksman is very nearly dropping bullets onto the target like mortar shells and must know the exact range within a few meters (and have the slug's trajectory memorized) if he is to hit anything at all. Fortunately, shotguns are normally used to hunt whitetail deer in the thick brush and briars of the south-eastern US or places like the Upper Peninsula of Michigan, where, due to the thick brush and briars, ranges tend to be very close--25 meters or less. At any range, shotgun slugs make massive and lethal wounds due to their tremendous mass. A typical 12 gauge shotgun slug is a blunt one-ounce hunk of metal--28 grams (432 grains); a typical 9 mm bullet is 115-135 grains (7 to 9 g) and cross-sectional area.

In the US, law enforcement agencies often use combat shotguns, especially for crowd and riot control where they may be loaded with less-than-lethal rounds such as rubber bullets or bean bags; this is the origin of the term "riot gun," which is a synonym for combat shotgun. The shotgun is also commonly used for home defense in the United States and Canada. It has excellent stopping power, is easier to aim than a handgun, and has an intimidating reputation for deadliness. When loaded with smaller shot, a shotgun will not penetrate walls as readily as bullets or slugs, making it safer for non-combatants when fired in or around populated structures.

Ammunition

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

• Shot is the most commonly used round, filled with lead or lead substitute pellets. Shot shells are described by the size of the pellets within. Size Eight is the smallest size used normally for hunting, and is used on small birds like doves. Size Two is the largest shot used for hunting normally, for large birds such as Canadian Geese. Steel shot is gauged differently, from 7 (smallest) to F (largest), since the lighter weight of steel requires larger pellets to achieve the same stopping power.
• Buckshot has become a less popular round over the last few decades. It is a shot round with pellets large enough to take down large game such as deer. The role of buckshot has been taken over by more efficient slug rounds. Buckshot is described by pellet size, from #4 (smallest) to #000 (largest). #000 and #00 are referred to as 'triple aught buck' and 'double aught buck' respectively.
• Slug rounds are rounds that fire a single solid slug. They are used for hunting large game.

Specialty ammunition

The ubiquitous nature of the shotgun has led to the development of a large variety of specialty shells, primarily for law enforcement. Types include:

• 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.
• Bean Bag rounds fire a nylon bag filled with tiny shots. The 'punch' effect of the bag is useful for knocking down aggressors and are used by police to subdue violent suspects. These rounds are sometimes used by wildlife officials to non-lethally subdue wild animals.
• Flechette rounds fire tiny aerodynamic darts instead of shot. These are useful in heavily foliaged areas, since plant cover is less likely to disperse the darts than round shot. These were used during the Vietnam War, under the name beehive rounds.
• Fireball or Dragon's Breath rounds fire a column of fiery sparks up to 250 feet (76 m) in length. They are intended to convert the shotgun into a single shot flamethrower. They are used by the United States Forest Service to start backfires. Their use on human targets would be considered inhumane.
• Disintegrator rounds are designed to blow out deadbolts, door locks and door hinges without risking the lives of those beyond the door. These rounds are packed with a dense metal powder, which can destroy a lock then immediately disperse. They are used by SWAT teams to quickly force entry into a locked room. Amongst police, these rounds are nicknamed 'master keys'.
• Cubic shot is lead shot with a cubic rather than spherical shape. The property of the shot's shape make it hard to be dispersed by foliage and very lethal to soft targets but with very little penetration. Cubic shot is useful for killing ground vermin in heavily foliaged areas, such as swamp rats.
• 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 600 feet (180 m).
• There are many other types of specialty ammunition available, including standard ammo variations such as explosive or armor-piercing rounds.

References

Elmer Keith (1950). Shotguns. Pennsylvania: The Stackpole Company. ISBN ASIN:B0006F7FY8

Bob Brister (1976). Shotgunning, The Art and the Science. New Jersey: New Win Publishing. ISBN 0-8329-1840-7

Michael McIntosh (1999). Best Guns. Alabama: Countrysport Press. ISBN 0-924357-79-4