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An air gun or airgun is a gun that uses energy from compressed air or other that are mechanically pressurized and then released to propel and accelerate , similar to the principle of the primitive blowgun. This is in contrast to a firearm, which shooting projectiles using energy generated via exothermic combustion (detonation) of chemical , most often black powder or smokeless powder.
Air guns come in both long gun ( air rifle) and handgun ( air pistol) forms. Both types typically propel metallic projectiles that are either diabolo-shaped pellets or spherical round shot called BBs, although in recent years Minié ball-shaped cylindro-conoidal projectiles called slugs are gaining more popularity. Certain types of air guns (usually air rifles) may also launch fin-stabilized projectile such as flechette (e.g., ) or hollow-shaft (so-called "airbows").
The first air guns were developed as early as the 16th century, and have since been used in hunting, shooting sport and even in warfare. There are three different power sources for modern air guns, depending on the design: spring-piston pump, pressure vesselN.A.R.Ser.1154-41-Ottawa-9 December 1941 or bottled gas (most commonly carbon dioxide and recently nitrogen).
Throughout 17th to 19th century, air guns in .30 to .51 were used to big-game hunting, deer and wild boar. These air rifles were charged using a pump to fill an air reservoir and gave velocities from . They were also used in warfare, the most recognized example being the Girandoni air rifle, a repeating rifle used by Austria in the 1788 war against Turkey.
At that time, they had compelling advantages over the primitive firearms of the day. For example, air guns could be discharged in wet weather and rain (unlike both matchlock and flintlock ), and discharged much faster than Muzzleloader. Moreover, they were quieter than a firearm of a similar caliber, had no muzzle flash, and were smokeless. Thus, they did not disclose the shooter's position or obscure the shooter's view, unlike the black powder muskets of the 18th and 19th centuries.
In the hands of skilled soldiers, they gave the military a distinct advantage. France, Austria and other nations had special sniper detachments using air rifles, mostly Jäger (infantry). The Austrian 1779 model was named Windbüchse (literally "wind rifle" in German). The gun was developed in 1768 or 1769Arne Hoff, Airguns and Other Pneumatic Arms, Arms & Armour Series, London, 1972 by the German Tyrol Ladins watchmaker, mechanic and gunsmith Bartholomäus Girardoni (1744–1799) and is sometimes referred to as the Girandoni air rifle or Girardoni air gun in literature (the name is also spelled "Girandony", "Giradoni"L.Wesley, Air Guns and Air Pistols, London 1955 or "Girardoni".H.L.Blackmore, Hunting Weapons, London 1971). Adopted by the Austrian leadership in 1779, the Windbüchse was about long and weighed , about the same size and mass as a conventional musket. The air reservoir was a removable, club-shaped, butt. The Windbüchse carried twenty-two .51 caliber (13 mm) lead balls in a tubular magazine. A skilled shooter could fire off one magazine in about thirty seconds. A shot from this air gun could penetrate a wooden board at a hundred paces, an effect roughly equal to that of a modern 9×19mm or .45 ACP caliber pistol.
Circa 1820, the Japanese inventor Kunitomo Ikkansai developed various manufacturing methods for guns, and also created an air gun based on the study of Western knowledge ("rangaku") acquired from the Netherlands in Dejima.
The Lewis and Clark Expedition (1804) carried a reservoir air gun, very likely the Girardoni, as it held 22 .46 caliber round balls in a tubular magazine mounted on the side of the gun barrel. The butt served as the air reservoir and had a working pressure of . The rifle was said to be capable of 22 aimed shots per minute and had a rifled bore of and a groove diameter .
One of the first commercially successful and mass-produced air guns was manufactured by the William F. Markham's Markham Air Rifle Company in Plymouth, Michigan, US. Their first model air gun was the wooden Challenger, marketed in 1886. In response, Clarence Hamilton from the neighboring Plymouth Air Rifle Company (later renamed to Daisy Manufacturing Company in 1895) marketed their all-metal Daisy BB Gun in early 1888, which prompted Markham to respond with their Chicago model in 1888 followed by the King model in 1890. The Chicago model was sold by Sears, Roebuck for 73 cents in its catalog. In 1928, the name of the Markham company was changed to King Air Rifle Company after the company was purchased by Daisy in 1916 after decades of intense competition, and continued to manufacture the "King" model air rifle until 1935 before ceasing operation altogether in the 1940s.
From the 1890s onwards, air rifles were used in Birmingham, England for competitive shooting sports. Matches were held in and working men's clubs, which sponsored shooting teams. This often took the form of Bell Target shooting, where the competitor aims to ring a bell by shooting through a small hole in a steel plate. Prizes, such as a leg of mutton for the winning team, were paid for by the losing team. During this time, over 4,000 air rifle clubs and associations existed across Great Britain, with as many as 1,600 in Birmingham alone. During this time, the air gun was associated with poaching because it could deliver a shot without a significant muzzle blast.
The increasing affordability of higher-power pre-charged pneumatic (PCP) rifles has allowed large projectiles and further target distance for competition purposes. For instance, the Extreme Benchrest competition held annually in Green Valley, Arizona allows calibers up to at 75 yd (68.58 m) while the Big Bore Benchrest arm of the same competition at other localities engages targets at .
Most spring-piston guns are single-shot by nature, but multiple-shot repeating rifle with magazine feeders have been introduced in recent years by manufacturers such as Gamo, Umarex and Hatsan.
Spring-piston guns, especially the high-powered "magnum" guns, are able to achieve muzzle velocities exceeding the speed of sound. The effort required for the cocking stroke is proportional to the designed power of the gun, with higher muzzle velocities requiring a stiffer spring and hence a greater cocking effort. Spring-piston guns have a practical upper limit of for .177 cal (4.5 mm) pellets, as higher velocities cause unstable pellet flight and loss of accuracy. This is due to the extreme buffeting caused when the pellet reaches and surpasses transonic speed, then slows back down and goes through sound barrier again, which is more than enough to destabilize the pellet's flight. Shortly after leaving the barrel, the supersonic pellet falls back below the speed of sound and the shock wave overtakes the pellet, causing its flight stability to be disrupted. Drag increases disproportionately as pellet velocity increases, so it is generally better to increase pellet weight to keep velocities subsonic in high-powered guns. Many shooters find that velocities in the range offer an ideal balance between power and accuracy.
Spring guns are typically cocked by one of the following mechanisms:
Spring-piston guns, especially high-powered ("magnum") models, do still recoil as a result of the mainspring pushing the piston forward. Although the recoil is less than that of some cartridge firearms, it can make the gun difficult to shoot accurately as the spring recoil is in effect while the pellet is still within the barrel. Spring gun recoil also has a sharp forward component, caused by the piston hitting the front end of the pump chamber when the spring has fully decompressed. These rapid double-jerking movements are known to damage telescopic sight not rated for spring gun usage. In addition, the spring often has unpredictable collateral transverse vibrations as well as torque, both of which can cause accuracy to suffer. These vibrations can be controlled by adding features like close-fitting spring guides or by aftermarket tuning done by gunsmiths who specialize in air gun modifications, a common one being the addition of high viscosity tenacious grease to the spring, which lubricates and serves to dampen vibration.
The better quality spring guns can have very long service lives, being simple to maintain and repair. Because they deliver the same mechanical energy output on each shot, external ballistics are quite consistent. Most Olympic Games air gun competitions through the 1970s and into the 1980s were shot with spring-piston guns, often of the opposing-piston recoil-eliminating type. Beginning in the 1980s, guns powered by compressed/liquefied carbon dioxide began to dominate the competition. Today, the guns used at the highest levels of competition are powered by compressed air.
Because of the need for cylinders or charging systems, PCP guns have higher initial costs but much lower operating costs when compared to CO2 rifles, and have superior performance over ordinary pump guns. Having no significant movement of heavy mechanical parts during the discharge cycle, PCP airgun designs produce lower recoil, and can shoot as many as 100 shots per charge depending on the tank/reservoir size. The ready supply of air has allowed the development of semi- and fully automatic air guns. PCP guns are very popular in Europe because of their accuracy and ease of use. They are widely utilized in ISSF 10 meter air pistol and rifle shooting events and the sport of Field Target shooting, and are usually fitted with .
Early stand pump designs encountered problems of fatigue (both human and mechanical), temperature warping, and condensation – none of which are beneficial to accurate shooting or the airguns' longevity. Modern stand pumps have multi-stage chambers and built-in air filtration systems and have overcome many of these problems. Using scuba set-quality air decanted from a diving cylinder provides consistently clean, dry, high-pressure air.
During the typical PCP's discharge cycle, the hammer of the rifle is released by the sear to strike the bash valve. The hammer may move rearwards or forwards, unlike firearms where the hammer almost always moves forward. The valve is held closed by a spring and the pressure of the air in the reservoir. The pressure of the spring is constant, and the pressure of the air released (which is also known as the working pressure) decreases with each successive shot. As a result, when the reservoir pressure is high, the valve opens less fully and closes faster than when the reservoir pressure is lower, resulting in a similar total volume of air flowing past the valve with each shot. This results in a degree of partial self-regulation that gives a greater consistency of velocity from shot to shot, which corresponds to the middle "plateau" phase of the gun's shot-to-shot muzzle velocity profile (also known as the power curve ). Well-designed PCP will display good shot-to-shot consistency over a long period, as the air reservoir is being depleted.
Other PCP rifles and pistols are regulated, i.e. the firing valve operates within a secondary chamber separated from the main air reservoir by the regulator body. The regulator maintains the pressure within this secondary chamber at a set pressure (lower than the main reservoir's) until the main reservoir's pressure drops to the point where it can no longer do so. As a result, shot-to-shot consistency is maintained for longer than in an unregulated rifle, and the gun can also output more shots due to reduced waste of reservoir pressure.
CO2 guns are popular for training, as the guns and ammunition are inexpensive, relatively safe to use, and no specialized facilities are needed for safety. In addition, they can be purchased and owned in areas where firearms possession is either strictly controlled or banned outright. Most CO2 powered guns are relatively inexpensive, and there are a few precision target guns available that use CO2.
It is also possible to power an HPA-compatible gun directly from a plug-in air compressor without using a gas cylinder, though this type of setup is rare.
The air cartridge system, both in the rifle and revolver forms, was at the peak of its popularity throughout the 1990s. The popularity of the Brocock range was such that, by 2002, estimates put the number of air cartridge guns in circulation around 70,000-80,000. However, a small number of incidents relating to the alleged illegal conversion of (mainly) Brococks to allow them to discharge live ammunition sparked a media frenzy. In early 2002, the BBC reported that figures from the National Criminal Intelligence Service showed converted Brococks accounted for 35 per cent of all guns recovered by the police, and David McCrone, firearms adviser to the Association of Chief Police Officers and Deputy Chief Constable of Greater Manchester Police, told the BBC's Newsnight "there is evidence which would justify banning them". After the UK government implemented the Anti-Social Behaviour Act 2003 in January 2004, it became illegal to possess such airguns without a firearm certificate in the United Kingdom. Brocock subsequently ceased production of all air cartridge systems and turned to focus primarily on PCP airguns.
By far the most popular shape is the diabolo pellet, which has two sections – a solid front portion called the "head", which contains the center of mass and is available in a variety of shapes and styles such as flat (wadcutter), round (domed), cone-shaped (pointed) and pitted (hollow point); and a hollowed, thin-walled conical rear portion called the "skirt", which expands and fully engages the bore to provide a good seal and thus allows maximal efficiency in pellet propulsion during shooting. In flight, the skirt has greater air drag-to-weight ratio than the head and exerts a rearward pull behind the center of mass, similar to that of a shuttlecock. This produces a phenomenon known as drag stabilization, which helps to counteract yawing and maintain a consistent flight path. However, the diabolo shape also means that the overall pellet will have poor ballistic coefficient and tends to lose energy quickly and be more unstable especially in the transonic region (272–408 m/s ~ 893–1340 ft/s).
Diabolo pellets are conventionally made from lead, but are widely available in non-lead alternatives, such as tin, or a combination of materials such as steel or gold alloys with polymer tips. A variety of lead-free pellets are offered by all major pellet manufacturers, including H&N Sport, RWS, JSB, Gamo, and others. Since lead is very dense, it has a higher ballistic coefficient than lightweight alternatives such as tin, copper, or plastic. At the present time, the airgun industry does not mass-produce dense alternatives to lead with a high ballistic coefficient for long-range shooting.
Due to the hardness of the steel, steel BBs cannot "take" to rifled barrels, which is why they are undersized (4.4 mm ball against 4.5 mm bore) to allow them to be used in .177" rifled barrels, which when used in this configuration can in effect be considered smoothbore, but with a poorer gas-seal, and if 4.5 mm diameter BBs are used, they would jam in the bore. Therefore, steel BBs lack the spin stabilization required for long-range accuracy, and usage in any but the cheapest rifled guns is discouraged. The softer lead BBs, however, can be used in rifled barrels.
Typically BBs are used for indoor practice, casual outdoor plinking, training children, or to save money, as they are significantly cheaper than pellets. Replica pistols allow people to train with a BB gun, saving a lot of money to centerfire firearm cartridges. Care should be exercised to avoid ricochet, and safety glasses are recommended. Recently, manufacturers have created Frangibility BBs, which break apart and do not ricochet, reducing the hazards associated with BB guns.
Some shotgunners use sightless BB rifles to train in instinctive shooting. Similar guns were also used briefly by the United States Army in a Vietnam-era instinctive shooting program called "Quick Kill". Time magazine, Friday, 14 July 1967
Some modern air guns are designed to discharge arrows and are called arrow guns or sometimes airbows. These arrows are designed with a hollow shaft that is open in the rear where the nock would normally be. When loaded, the hollow arrow shaft is slid rearwards over a barrel whose external diameter is only fractionally smaller than the shaft's interior diameter, providing a close-enough fitting that minimizes rattling and gives a reasonable enveloping seal without causing too much friction. During shooting, the trigger releases high-pressure air from the barrel to the front portion of the hollow arrow shaft, pushing the arrow forward. Such air guns can shoot arrows at launch velocities rivalling or even exceeding high-end , while retaining consistency of precision unaffected by archer's paradox, but they are also more expensive to set up and maintain.
Other less common traditional calibers include:
Larger caliber air rifles suitable for hunting large animals are offered by major manufacturers. These are usually PCP guns. The major calibers available are:
Custom air guns are available in even larger calibers such as 20 mm (0.79") or .87 (22.1 mm).
For reason of safety and security a rule of use of the safety flag has been strictly mentioned by ISSF for the 10m air pistol and rifle shooting sports events.
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