View source for Air gun

{{short description|Device that uses compressed air to fire projectiles}}
{{other uses}}
{{about-distinguish-text|air guns in general|[[Airsoft gun]]s, a specific type of air gun}}
{{Use dmy dates|date=November 2023}}
[[File:2014 Wound Warrior Team Navy Trials 140604-N-ZO696-018.jpg|thumb|A [[Parasports|para-athlete]] competing with a [[ISSF 10 meter air rifle|match air rifle]]]]
[[File:Under Lever Spring Piston Air Rifles.jpg|thumb|A collection of [[lever-action]], spring-piston air rifles]]

An '''air gun''' or '''airgun''' is a [[gun]] that uses [[compressed air]] or other pressurized [[gas]]es to fire [[projectile]]s, reminiscent of the principle behind the ancient [[blowgun]]. This is in contrast to a [[firearm]], which shoots projectiles using pressure generated via [[combustion]] of a chemical propellant, most often [[black powder]] in antique firearms and [[smokeless powder]] in modern firearms.

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 [[pellet (air gun)|pellet]]s or spherical [[round shot|shot]]s called [[BB (ammunition)|BB]]s, although in recent years [[Minié ball]]-shaped [[cylindro-conoidal bullet|cylindro-conoidal projectile]]s called [[slug (projectile)|slug]]s are gaining more popularity. Certain types of air guns (usually air rifles) may also launch [[fin]]-stabilized projectile such as [[flechette|dart]]s (e.g., [[tranquilizer gun]]s) or hollow-shaft [[arrow]]s (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 (device)|spring]]-[[piston pump|piston]], [[pressure vessel|pneumatic]]<ref>N.A.R.Ser.1154-41-Ottawa-9 December 1941</ref><ref>{{Cite web|url=https://www.scribd.com/document/402903841/N-6174-Intelligence-Circular-No-13-18-November-1942-pdf|title=N-6174 Intelligence Circular No. 13 - 18 November 1942 PDF &#124; PDF &#124; Anti Aircraft Warfare &#124; Regiment|website=Scribd|accessdate=28 May 2025}}</ref> or [[bottled gas|bottled compressed gas]] (most commonly [[carbon dioxide]] and recently [[nitrogen]]).

==History==
[[Image:KunitomoAirGun.jpg|thumb|[[Kunitomo air gun]] developed by the Japanese inventor [[Kunitomo Ikkansai]], {{c.|1820–1830}}]]
Air guns represent the oldest [[pneumatics|pneumatic]] technology. The oldest existing mechanical air gun dates back to about 1580, and is currently kept in the [[Livrustkammaren]] Museum in [[Stockholm]]. This is approximately what most historians recognize as the beginning of the modern air gun.

Throughout 17th to 19th century, air guns in .30 to .51 [[caliber]]s were used to [[big-game hunting|hunt big game]], [[deer]] and wild [[boar]]. These air rifles were charged using a pump to fill an air reservoir and produced velocities from {{cvt|650|to|1000|ft/s}}. 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]] [[musket]]s), and discharged much faster than [[Muzzleloader|muzzle-loading guns]].<ref name="Philip 2006">{{cite journal|last=Schreier|first=Philip|title=The Airgun of Meriwether Lewis|journal=American Rifleman|date=October 2006|url=http://www.americanrifleman.org/article.php?id=14049&cat=3&sub=0|access-date=23 December 2013|archive-url=https://web.archive.org/web/20131205182127/http://www.americanrifleman.org/article.php?id=14049&cat=3&sub=0|archive-date=5 December 2013}}</ref> Moreover, they were quieter than a firearm of a similar caliber and produced no muzzle flash or smoke cloud when fired. Thus, they did not give away 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 1769<ref>Arne Hoff, ''Airguns and Other Pneumatic Arms'', Arms & Armour Series, London, 1972</ref> by the [[German Tyrol|Tyrolean]] [[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"<ref>L.Wesley, ''Air Guns and Air Pistols'', London 1955</ref> or "Girardoni".<ref>H.L.Blackmore, ''Hunting Weapons'', London 1971</ref>). Adopted by the Austrian leadership in 1779, the ''Windbüchse'' was about {{cvt|4|ft|m|1}} long and weighed {{convert|10|lb}}, about the same size and mass as a conventional [[musket]]. The air reservoir was a removable, club-shaped, [[stock (firearm)|butt]]. The ''Windbüchse'' carried twenty-two .51 [[caliber]] (13&nbsp;mm) lead balls in a tubular [[magazine (firearms)|magazine]]. A skilled shooter could fire off one magazine in about thirty seconds. A shot from this air gun could penetrate a {{convert|1|in|cm|spell=in|adj=mid|-thick}} 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|Dutch]] in [[Dejima]].
[[Image:KunitomoAirGunMechanism.jpg|thumb|Kunitomo air gun trigger mechanism]]

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|barrel]]. The butt served as the air reservoir and had a working pressure of {{convert|800|psi|bar|abbr=on}}. The rifle was said to be capable of 22 aimed shots per minute and had a rifled bore of {{convert|0.452|in|abbr=on}} and a groove diameter {{convert|0.462|in|abbr=on}}.

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 Outdoor Products|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,<ref>{{cite journal|last=Laidlaw|first=Angus|title=Chicago Air Rifle Markham's Patent|journal=American Rifleman|date=January 2014|volume=162|issue=1|page=48}}</ref> 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|target shooting]].<ref name="Spittle">{{cite web |author1=Frank Spittle |title=Bell Target Story |url=http://www.belltarget.com/resources/Bell_Target_Story.pdf |website=Bell Target Shooting |access-date=28 March 2023 |archive-url=https://web.archive.org/web/20220419154427/http://www.belltarget.com/resources/Bell_Target_Story.pdf |archive-date=19 April 2022 |pages=2–9 |language=English |date=23 July 2008 |url-status=live}}</ref> Matches were held in [[public house]]s and [[working men's club]]s, 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.<ref>{{cite web |title=Bell Target Shooting |url=http://www.belltarget.com/ |website=Bell Target Shooting |access-date=28 March 2023 |archive-url=https://web.archive.org/web/20230311083833/http://www.belltarget.com/ |archive-date=11 March 2023 |language=English |url-status=live}}</ref> Prizes, such as a leg of [[Lamb and mutton|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.<ref name="Spittle"/> During this time, the air gun was associated with [[poaching]] because it could deliver a shot without a significant [[muzzle blast|muzzle report]].{{Citation needed|date=March 2023}}

==Use==
Air guns are used for [[game (hunting)|hunting]] (small to medium game), [[pest control]], recreational [[shooting]] (commonly known as [[plinking]]) and competitive sports such as the [[Shooting at the Summer Olympics|Olympic]] [[ISSF 10 meter air rifle|10 m air rifle]] and [[ISSF 10 meter air pistol|10 m air pistol]] events. [[Field target]] (FT) is a competitive form of [[metallic silhouette shooting]] in which the targets are animal-shaped steel [[Shooting target|targets]] with a "kill zone" cut-out. [[Hunter field target]] (HFT) is a variation, using identical equipment, but with differing rules. The distances FT and HFT competitions are shot at range between {{convert|7.3|and|41.1|m}} for HFT & {{convert|7.3|and|50.29|m}} for FT, with varying sizes of "reducers" being used to increase or decrease the size of the kill zone.  In the UK, competition power limits are set at the legal maximum for an unlicensed air rifle, i.e. {{convert|12|ftlbf|J|abbr=on|lk=in}}. Air rifle benchrest is an international shooting sport where the objective is to hit a (small) bulls eye target at {{convert|25|m|yd|2|abbr=on|lk=in}} shooting distance. There are two divisions ARLV {{convert|12|ftlbf|J|2|abbr=on|lk=in}} and ARHV {{convert|20|ftlbf|J|2|abbr=on|lk=in}}.<ref>{{Cite web|url=http://wrabf.com/rules/WRABF%20&%20ERABSF%20RULEBOOK%202013-%202021.pdf|title=WORLD RIMFIRE & AIR RIFLE BENCHREST FEDERATION (WRABF)& EUROPEAN RIMFIRE & AIR RIFLE BENCHREST SHOOTING FEDERATION(ERABSF)OFFICIAL RULE BOOK 2013-2021|accessdate=28 May 2025}}</ref><ref>{{Cite web|url=http://www.wrabf.com/WRABF%20Targets.htm|title=WRABF|accessdate=28 May 2025}}</ref>

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 {{convert|.30|in|mm}} at 75 yd (68.58 m) while the Big Bore Benchrest arm of the same competition at other localities engages targets at {{convert|35|to|300|yd|m}}.

== Powerplant ==
The component of an airgun that provides the gas pressure needed to propel projectiles is called its ''powerplant'', which uses internally stored pressurized gas; and ''compressed gas'' (most commonly [[carbon dioxide|CO<sub>2</sub>]]), which uses external sources of pressurized gas.<ref name=airguntypes>{{cite web |url=http://www.airguns.net/general_airgun_types.php |title=The Three Basic Types of Airguns |author=Ben Saltzman |publisher=American Airguns |access-date=14 September 2007| archive-url= https://web.archive.org/web/20071015143244/http://airguns.net/general_airgun_types.php| archive-date= 15 October 2007 | url-status= live}}</ref>

=== Spring-piston ===
[[File:Air rifle collection 2.jpg|thumb|Variety of different types & models of spring piston & gas ram air guns]]
A '''spring-piston air gun''' (also known as a '''spring gun''' or simply a "'''springer'''") operates by means of a [[spring (device)|spring]]-loaded [[piston pump]] assembly contained within a compression chamber separate from the [[gun barrel]]. Traditionally, a [[grease (lubricant)|grease]]-lubricated steel [[coil spring]] is used as the powerplant main spring.  Before shooting, the user needs to manually cock the gun by flexing a lever connected to the pump assembly, which pulls the pump piston rearwards and compresses the main spring until the rear of the [[piston]] engages the [[sear (firearm)|sear]].  When shooting, the [[trigger (firearms)|trigger]] is pulled and disengages the sear, allowing the main spring to decompress and release its stored [[elastic potential energy]], pushing the piston forward, thereby compressing the air in the pump cylinder.  Because the pump outlet (located to the front of the pump) is directly behind the pellet seated in the barrel [[chamber (firearms)|chamber]], once the air pressure has risen enough to overcome the [[static friction]] and/or barrel restriction holding back the pellet, the pellet is propelled forward by an expanding column of pressurized air.  All this takes place in a fraction of a second, during which the air undergoes [[adiabatic process#Adiabatic heating and cooling|adiabatic heating]] to several hundred degrees and then cools as the air expands.  This can also cause a phenomenon referred as "dieseling", where flammable substances in the compression chamber (e.g., petroleum-based lubricant) can be [[compression ignition|ignited by the compression heat]] like in a [[diesel engine]], and lead to an [[afterburner]] effect with (often unpredictable) additional thrusts.  This often results in combustion smoke coming out of the [[muzzle (firearm)|muzzle]] and potential pressure damage to the rubber [[O-ring]] [[seal (mechanical)|seal]]s inside the gun. Dieseling can be made to occur ''intentionally'' to increase power, by coating the pellet with lubricant or [[petroleum jelly]], although this may result in damage to the breech seal.

Most spring-piston guns are [[single-shot]] [[breechloader]]s by nature, but multiple-shot [[repeating rifle|repeater]]s with [[magazine (firearms)|magazine]] feeders have been introduced in recent years by manufacturers such as [[Gamo (airgun manufacturer)|Gamo]], [[Umarex]] and Hatsan.
[[File:Air Pistol.jpg|thumb|Spring Piston Air Pistols]]

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 {{convert|1250|ft/s|m/s|abbr=on}} for [[.177 caliber|.177 cal]] (4.5&nbsp;mm) pellets, as higher velocities cause unstable pellet flight and loss of accuracy. This is due to the extreme [[Aeroelasticity#Buffeting|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 {{convert|800|-|900|ft/s|m/s|abbr=on}} range offer an ideal balance between power and accuracy.

Spring guns are typically cocked by one of the following mechanisms:
* Break-barrel — like a [[break action]] firearm, the barrel is hinged at the junction with the [[receiver (firearms)|receiver]] and is flexed downwards to expose the [[breech (firearms)|breech]] and serves as the cocking lever
* Fixed-barrel – the barrel is fixed to the receiver, and the cocking is done with a separate cocking lever
** Underlever – the cocking lever is located underneath the barrel or the receiver and is flexed downwards during cocking
** Sidelever – the cocking lever is located to the side (usually the right side) of the receiver and is flexed sideways during cocking
** Overlever – the cocking lever is located above the barrel and is flexed upwards during cocking, seen in some air pistols
* Motorized cocking powered by a rechargeable battery (rare)

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)|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|scopes]] not rated for spring gun usage. In addition, the spring often has unpredictable collateral transverse vibrations as well as [[torque|torquing]], 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.{{citation needed|date=November 2019}} Most [[Olympic Games|Olympic]] [[ISSF shooting events|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]].

==== Gas spring ====
Some newer generation air guns incorporate a [[gas spring]] (commonly referred to as a ''gas piston'', ''gas ram'', ''gas strut'' or ''nitro piston'') instead of a mechanical spring. The spring itself is essentially a stand-alone enclosed [[piston pump]] without outlets and with pressurized air or [[inert gas]] (such as [[nitrogen]]) held tightly sealed within the [[cylinder (engine)|cylinder]]. When the gun is cocked, the gas inside the cylinder gets further compressed by the piston, stores [[potential energy]] and acts as a [[pneumatic]] [[accumulator (energy)|accumulator]]. Gas spring units require higher precision to manufacture since they require a low-friction sliding seal that can withstand the high pressures within when cocked. The advantages of the gas spring include the ability to keep the gun cocked and ready to fire for extended periods of time without long-term spring [[fatigue (material)|fatigue]], no twisting [[torque]] (caused by coil spring expanding) exerted onto the gun, smoother recoil pattern and faster "lock time" (the time between pulling the trigger and the pellet being discharged), which all result in more consistent accuracy.  Gas springs perform more reliably in cold climates than coil springs, because metallic coil springs need to be coated with [[grease (lubricant)|lubricating grease]] which often thickens in low temperatures causing the gun to "freeze up".  Gas springs also have less lateral and longitudinal vibrations than coil springs, hence are usually less "hold-sensitive", making it easier to achieve consistent [[shot grouping]]s.

=== Pneumatic ===
[[File:New Benelli Kite.jpg|thumb|An example of a [[Benelli Kite]] pre-charged pneumatic air pistol, as used in [[10 m Air Pistol|10 metre air pistol]] [[ISSF shooting events]]]]
Pneumatic airguns propel the projectiles by utilizing the [[compressed air energy storage|pneumatic potential energy]] within [[compressed air]], which is pressurized beforehand and stored inside the gun, and then released through valves during shooting. Single-stroke and multi-stroke pump guns utilize an on-board [[hand pump]] to pressurize air in an internal [[pressure vessel|reservoir tank]], while pre-charged pneumatic guns' reservoirs are filled from an external source using either a high-pressure [[bicycle pump#Stand pump|stand pump]] or by decanting air from a larger [[diving cylinder]].

====Pump pneumatic====
'''Pump pneumatic air gun'''s, or '''pump gun'''s, use a lever-operated onboard air pump to pressurize an internal reservoir, and then discharge the stored compressed air during shooting. Depending on the design, pump guns can be either single-stroke or multi-stroke.

* In ''single-stroke'' pneumatic air guns (also known as "single pump") a single motion of the cocking lever is all that is required to mechanically compress the air. The single-pump system has always dominated the casual plinking market, and is usually found in target rifles and pistols, where the higher muzzle energy of a multi-stroke pumping system is not required. Single-stroke pneumatic rifles dominated the national and international [[International Shooting Sport Federation|ISSF]] [[ISSF shooting events|10 metre air rifle shooting events]] from the 1970s to the 1990s, until being outperformed by the introduction of pre-charged pneumatic (PCP) guns (discussed [[#Pre-charged pneumatic|below]]).
* ''Multi-stroke'' pneumatic air guns (also known as "multi-pump") use multiple pumpings to achieve variable power levels in order to adapt for both long or short-range shooting. These air guns are usually single-shot, where each shot requires approximately 5 strokes. However, up to five shots are possible, usually requiring approximately 10 to 20 strokes, as long as the air reservoir is capable of storing higher pressure. For safety reasons, most multi-stroke guns are usually designed to have their pump lever jam when the reservoir has reached its maximum pressure limit, so the user can no longer pump the gun until it's discharged. The maximum pressure limit for the reservoir is approximately 20 to 30 strokes.

====Pre-charged pneumatic====
[[Image:20ozCO2Condor.JPG|thumb|Airforce Condor, one of the most powerful PCP air rifles on the market]] 
'''Pre-charged pneumatic air guns''' or '''PCP''' have their internal reservoir pre-filled from an external air source (such as a [[diving cylinder]] or [[air compressor]], or by manual charging with a high-pressure [[bicycle pump#Stand pump|stand pump]]), and remain pressurized until depleted after repeated shooting. During shooting, the hammer strikes the reservoir's release valve, allowing a set volume of the pressurized air to be discharged into the chamber and propel the projectile.  Depending on the release valve design, PCP air guns can be categorized into two types – ''unregulated'' and ''regulated'' (which has either a mechanical or electronic [[pressure regulator|regulator]] valve). In addition to [[compressed air]], custom PCP models using compressed pure [[nitrogen]] and even compressed [[helium]] have also been recently developed.

[[File:Walther LG400 FT England.jpg|thumb|[[Field Target]] variant of a [[Walther LG400]] PCP Air Rifle.]]
Because of the need for cylinders or charging systems, PCP guns have higher initial costs but much lower operating costs when compared to CO<sub>2</sub> 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.<ref>{{cite web|url=http://air-ordnance.com/smg-22-p-938.html|title=Air Ordnance Full Auto Pellet Gun|access-date=28 November 2014|archive-url=https://web.archive.org/web/20141203213004/http://air-ordnance.com/smg-22-p-938.html|archive-date=3 December 2014|url-status=dead}}</ref> PCP guns are very popular in [[Europe]] because of their accuracy and ease of use. They are widely utilized in [[ISSF shooting events|ISSF 10 meter air pistol and rifle shooting events]] and the sport of [[Field Target]] shooting,<ref>{{cite web|url=http://www.aafta.org|title=American Airgun Field Target Association|access-date=28 November 2014}}</ref> and are usually fitted with [[telescopic sight]]s.

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|scuba]]-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.<ref>{{cite journal |last1=Tavella |first1=Domingo |title=Ballistics of PCP Airguns |journal=Octanti Associates Inc |date=July 2018 |url=https://www.researchgate.net/publication/326191398}}</ref>

=== Compressed gas ===
[[File:BB gun with CO2 and BBs.jpg|thumb|right|200px|CO<sub>2</sub> pistol and disposable [[Powerlet]] cylinders]]
[[File:Nitrogen tank.jpg|thumb|250px|A Pure Energy N<sub>2</sub> tank with a remote line attached]]
'''Compressed gas guns''', also known as ''CG guns,''<ref>{{cite web|url=http://www.pyramydair.com/article/What_About_CO2_December_2003/6|title={{CO2}} is used to power many air guns|publisher=PyramydAir|author=Tom Gaylord|access-date=15 January 2017}}</ref> are essentially pneumatic airguns utilizing detachable [[pressure vessel|pressure reservoir]]s in the form of prefilled external [[gas cylinder]]s (often with built-in [[pressure regulator|regulator valve]]s), and are commonly referred to as ''CO<sub>2</sub> guns'' due to the ubiquitous commercial use of [[bottled gas|bottled]] [[liquid carbon dioxide]].  However, more recent high-end models sometimes use larger [[compressed air]]/[[nitrogen]] (known as HPA or "N<sub>2</sub>") cylinders, which have higher operating pressures and better thermal stability.

==== CO<sub>2</sub> ====
[[File:Walther CP88 Schall.jpg|thumb|[[Walther CP 88]] CO<sub>2</sub> pistol with adapted silencer]]
[[File:Crossman-2240.jpg|thumb|Crosman 2240 CO<sub>2</sub> one shot pistol, (.22 pellet caliber)]]
'''CO<sub>2</sub> guns''', like other pneumatic guns using compressed air, offer power for repeated shots in a compact package without the need for complex pumping or filling mechanisms. The ability to store power for repeated shots also means that repeating arms are possible. There are many replica revolvers and semi-automatic pistols on the market that use CO<sub>2</sub> power.  Most CO<sub>2</sub> guns use a disposable cylinder called a "[[Powerlet]]" cartridge, that is often purchased with {{convert|12|g|oz}} of pressurized CO<sub>2</sub> gas, although some, usually more expensive models, use larger refillable CO<sub>2</sub> reservoirs like those typically used with [[paintball marker]]s.

CO<sub>2</sub> 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 CO<sub>2</sub> powered guns are relatively inexpensive, and there are a few precision target guns available that use CO<sub>2</sub>.

==== High-pressure air ====
[[High-pressure air]] (HPA) system, or ''N<sub>2</sub>'', was originally developed for [[paintball markers]] as a replacement for CO<sub>2</sub> cartridges, and uses Powerlet interface-compatible [[diving cylinder]]s filled with either pure [[nitrogen]] or [[compressed air]] (which is 78% nitrogen). Because nitrogen is more [[chemically inert|inert]] than CO<sub>2</sub>, it remains in the [[gas]]eous state longer when compressed; when it expands, it cools due to the [[Joule-Thomson effect]] but at a far lower rate than [[liquid carbon dioxide|liquid CO<sub>2</sub>]] because there is no change in [[state of matter|state]] [[boiling|from liquid to gas]]. This [[thermostability]] reduces the variation in output pressure associated with rapid successions of firing cycles, improving accuracy and reliability in extreme climates. However, because compressed air is stored at higher pressures (up to {{cvt|34|MPa|disp=or|lk=on}}) than liquid CO<sub>2</sub> (stored at around {{cvt|8|MPa|disp=or}}), HPA cylinders are more expensive. Cylinders smaller than {{cvt|1.1|L|cuin|lk=on}} may not even last as long as a standard CO<sub>2</sub> cartridge when subjected to frequent uses.

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.

====Air cartridge system====
First developed in the [[United Kingdom]] during the 1980s as the Saxby-Palmer Ensign,<ref>{{cite web|url=https://www.pyramydair.com/blog/2006/01/brocock-air-cartridges/|title=Brocock air cartridges|last=Gaylord|first=Tom|date=18 January 2006|publisher=Pyramyd Air Blog|access-date=25 July 2021}}</ref> and then by Brocock as the "Brocock Air Cartridge System" (BACS) and later into the "Tandem Air Cartridge" (TAC),<ref name="BACS">{{cite web|url=https://www.airgunmagazine.co.uk/features/air-cartridge-system-10-years-later/|title=The air cartridge system – 10 years on|last=Cross|first=Rupert|date=1 September 2013|publisher=Airgun Shooter Magazine|access-date=25 July 2021}}</ref> this variation of the pre-charged pneumatic design have no pressure reservoir built into the gun, but instead use removable and reusable metallic [[gas cylinder]]s often known as "Brocock cartridges" after its British manufacturer.  Each air cartridge is essentially a self-contained gas reservoir housed inside a [[cartridge case]] (usually in the size of a [[.38 Special]]), with an internal [[bash valve]] designed to release the content when the base of the cartridge is struck. Prior to shooting, each cartridge is pre-filled with sufficient [[compressed air]] for one shot (typically via a multi-stroke [[hand pump]]) and has a [[.177 caliber|.177]]/[[.22 caliber]] pellet pre-seated to its front slot, and the entire cartridge is then inserted into a [[chamber (firearms)|chamber]] in the [[gun barrel]]. When shooting, the [[hammer (firearms)|hammer]] hits the rear of the air cartridge, mimicking the function of a [[centerfire ammunition]]. This allows the airgun to be constructed and operated in similar fashions to genuine firearms. It also allows for higher shot consistency because each cartridge can be easily filled to an identical air charge, essentially removing the "power curve" of conventional PCP guns and bypassing any need for [[pressure regulator|regulator]]s. It also simplifies the magazine feed design and eliminates the risk of deforming the projectiles when the [[action (firearms)|action]] seats each pellet, as the soft lead pellet is protected from contact with the action probe by the harder cartridge casing.

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.<ref name="BACS"/> However, a small number of incidents relating to the alleged illegal conversion of (mainly) Brococks to [[improvised firearms|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,<ref>{{cite web|url=https://news.bbc.co.uk/2/hi/uk_news/england/1779349.stm|title=Live-bullet airgun a 'major problem'|last=|first=|date=24 January 2002|publisher=BBC News|access-date=25 July 2021}}</ref> 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.

==Ammunition==
===Pellet===

{{Main|Pellet (air gun)}}
[[File:Diabolo prof.jpg|thumb|Wadcutter or Flathead pellets]]
The most popular ammunition used in rifled air guns is made of lead, a [[Heavy metals|heavy metal]]. Lead is [[Lead poisoning|highly poisonous]] (whether inhaled or swallowed), affecting almost every organ and system in the human body. For this reason, lead-free pellets are becoming increasingly popular, and are available in all major shapes and styles, just like traditional lead pellets.

By far the most popular shape is the [[wasp-waist]]ed '''[[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 (mechanical)|seal]] and thus allows maximal efficiency in pellet propulsion during shooting.  In flight, the skirt has greater [[air drag|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 [[yaw (rotation)|yaw]]ing 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 [[External ballistics#Transonic problem|transonic region]] (272–408&nbsp;m/s ~ 893–1340&nbsp;ft/s).

[[Image:177cal.jpg|thumb|250px|A .177 (4.5mm) caliber "Wadcutter" pellet next to a stick of chewing gum]]
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.<ref>{{Cite web |title=Home - Lead Free Pellets |url=https://www.leadfreepellets.org/ |access-date=2 May 2022 |website=www.leadfreepellets.org}}</ref> 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.

==== Slug ====
Some manufacturers also have recently introduced the more [[cylindro-conoidal bullet|cylindro-conoidal]]-shaped "[[slug (projectile)|slug]]" pellets for the more powerful modern PCP air rifles. Compared to the commonly used diabolo pellets, these slug pellets resemble [[cast bullet]]s and have more contact surface with the bore and hence need greater propelling force to overcome friction, but have better [[aerodynamics]], [[ballistic coefficient]], and longer effective ranges due to the more aerodynamic shape, however they also require a fully [[rifling|rifled]] barrel for spin stabilization in flight. Appropriately sized bullets cast from firearm bullet molds can be used in big bore air rifles.
Caution should be used when handling lead projectiles or preparing animals for food, as lead fragments can be easily missed inside the meat. Lead-free slugs in airgun calibers are gradually being developed and becoming available for purchase from manufacturers such as Zan Projectiles, due in part to regulations on hunting with lead projectiles in many areas.

===BB===
[[Image:BB copper and nickel plated.jpg|thumb|right|200px|Steel BBs coated with copper and nickel]]
{{Main|BB gun}}
The BB [[shot (pellet)|shot]] was once the most common airgun ammunition in the US, thanks to the popularity of [[Daisy Outdoor Products|Daisy]]'s line of BB airguns. A BB is a small metallic ball in 4.5&nbsp;mm/[[.177 caliber|.177" diameter]], typically made of steel (with a copper or zinc coating) or lead. Originally called the "[[round shot]]", the contemporary name came from the [[shot (pellet)#Lead shot comparison chart|"BB"- size]] lead [[birdshot]] used in [[shotgun shell]]s, which the first BB gun invented in 1886 was designed to shoot. Steel BBs can be acceptably accurate at short distances when fired from properly designed [[BB gun]]s with [[smoothbore]] barrels. Lead #3 buckshot pellets can be used in .25" caliber airguns as if they were large BBs.

Due to the hardness of the steel, steel BBs cannot "take" to rifled barrels, which is why they are undersized (4.4&nbsp;mm ball against 4.5&nbsp;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&nbsp;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 {{CO2}} 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|frangible]] BBs,<ref>{{Cite web |title=Air Venturi Dust Devil Mk2 Frangible BBs, 1,500 ct. {{!}} Pyramyd Air |url=https://www.pyramydair.com/product/air-venturi-dust-devil-frangible-bbs-1-500-ct?p=1477 |access-date=2 May 2022 |website=www.pyramydair.com |language=en}}</ref> 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 "[[Point shooting#Rifle Quick Kill|Quick Kill]]".<ref>''Time'' magazine, Friday, 14 July 1967</ref>

===Darts and arrows===
[[File:LG Bolzen.jpg|thumb|Darts for an air gun]]
In the 18th and 19th centuries, air gun darts were popular, largely because they could be reused. Although less popular now, several different types of darts are made to be used in air guns, but it is not recommended that darts be used in air guns with [[rifling|rifled]] bores or in spring-powered air guns.<ref>{{cite web|url=http://www.beemans.net/airgun_projectiles.htm|title= Airgun projectiles|access-date=1 June 2017}}</ref> Air guns that shoot darts are sometimes called ''dart guns'', and ''[[tranquilizer gun]]s'' if the darts used are loaded with [[anesthetic]] ([[tranquilizer]]) compounds.

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 (arrow)|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 (mechanical)|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 [[crossbow]]s, while retaining consistency of precision unaffected by [[archer's paradox]], but they are also more expensive to set up and maintain.

=== Laser beam ===
The [[modern pentathlon]] has since 2009 included a [[laser-run]] event that replaced the traditional cross country run of 3,200 metres and timed air-pistol shoot.<ref>{{Cite web|last1=Pesca|first1=Mike|date=11 August 2012|title=Modern Pentathlon Hot-Shots: These Ladies Have Laser Pistols|url=https://www.npr.org/sections/thetorch/2012/08/11/158634634/modern-pentathlon-hot-shots-these-ladies-have-laser-pistols|access-date=4 August 2021|website=NPR.org|language=en}}</ref> The competitors run 4 laps of 800 m combined with 4 rounds of firing.  The pistols used are modified air pistols that fire an eye-safe laser beam towards a target at the same time as a discharge of air. This has made the organisation of the events easier from a safety point of view and allows competitors to travel more easily with their weapons.<ref>{{Cite magazine|title=Lasers Make Modern Pentathlon More Modern|language=en-US|magazine=Wired|url=https://www.wired.com/2012/08/modern-pentathlon-laser-pistols/|access-date=4 August 2021|issn=1059-1028|date=11 August 2012}}</ref>

===Airsoft pellets===
[[Airsoft pellets]] are plastic BBs shot from [[airsoft guns]].

==Calibers==
The most common air gun [[caliber]]s are
* [[.177 caliber|.177]] (4.5&nbsp;mm): the most common caliber. Mandated by the ISSF for use in international target shooting competition at 10m, up to Olympic level in both rifle and pistol events. It has also been adopted by most National Governing Bodies for domestic use in similar target shooting events. It has the flattest trajectory of all the calibers for a given energy level. At suitable energy levels it can be used effectively for hunting.
* [[.22 caliber|.22]] (5.5&nbsp;mm & 5.6&nbsp;mm): for hunting and general use. In recent years air rifles and pistols in .22" (and some other calibers) have been allowed for use in both domestic and international target shooting in events not controlled by the ISSF. Most notably in FT/HFT and Smallbore Benchrest competitions. These events often allow the use of any caliber air gun, up to a maximum which is often .22", rather than a fixed caliber.

Other less common traditional calibers include:
* [[5 mm caliber|.20]] (5&nbsp;mm): initially proprietary to the Sheridan multi-pump pneumatic air rifle, later more widely used. 
* [[.25 caliber|.25]] (6.35&nbsp;mm): the largest commonly available caliber for most of the 20th century.
* [[.30 caliber|.30]] (7.62&nbsp;mm): the current largest available for non-PCP powered airguns

Larger caliber air rifles suitable for hunting large animals are offered by major manufacturers. These are usually PCP guns. The major calibers available are:
* [[9 mm caliber|.357]] (9mm)
* [[.45 caliber|.45]] (11.43&nbsp;mm)
* [[.50 caliber|.50]] (12.7&nbsp;mm)
* [[.58 caliber|.58]] (14.5&nbsp;mm)
* [[.72 caliber|.72]] (18.28&nbsp;mm)

Custom air guns are available in even larger calibers such as [[20 mm caliber|20 mm]] (0.79") or .87 (22.1&nbsp;mm).

== Legislation ==
{{Main|Air gun laws}}
While in some countries air guns are not subject to any specific regulation, in most, there are laws which differ widely. Each jurisdiction has its definition of an air gun. Regulations may vary for weapons of different bore, [[muzzle energy]], [[Muzzle velocity|velocity]], or ammunition material. Guns designed to fire [[pellet (air gun)|metal pellets]] are often more tightly controlled than [[airsoft]] weapons. There may be a minimum age for possession, and sales of both air guns and ammunition may be restricted. Some areas require permits and background checks similar to those required for propellant type firearms.

==Safety and misuse==
While historical air guns have been made specifically for warfare, modern air guns can also be deadly.<ref name="Stuff.co.nz_3916775">{{cite web |url=http://www.stuff.co.nz/national/crime/3916775/Crackdown-on-killer-air-rifles |title=Crackdown on killer air rifles |date=14 July 2010 |work=[[NZPA]] |access-date=15 September 2011}}</ref> In medical literature, modern air guns have been noted as a cause of death.<ref>{{cite journal|title=Air gun--a deadly toy?: A case report. | pmid=16683474 | volume=46 | issue=2 | journal=Med Sci Law | pages=177–80 | last1 = Kuligod | first1 = FS | last2 = Jirli | first2 = PS | last3 = Kumar | first3 = P| s2cid=2496377 | year=2006 | doi=10.1258/rsmmsl.46.2.177 }}</ref><ref>{{cite journal|title=Fatal nonpowder firearm wounds: case report and review of the literature. | pmid=2104975 | volume=85 | issue=2 | journal=Pediatrics | pages=177–81 | last1 = Lawrence | first1 = HS| year=1990 | doi=10.1542/peds.85.2.177 | s2cid=20875059 }}</ref><ref>{{cite journal|url= |title=Air weapon injuries: a serious and persistent problem.|journal=Archives of Disease in Childhood|volume=86|issue=4|pages=234–235|doi=10.1136/adc.86.4.234|pmid=11919092|year=2002|last1=Ceylan|first1=H.|pmc=1719169}}</ref> This has been the case for guns of caliber .177 and .22 that are within the legal muzzle energy of air guns in the United Kingdom.<ref>{{cite journal|title=Air Weapon Fatalities | pmc=500806 | pmid=9797730|volume=51|issue = 7|year=1998|journal=J. Clin. Pathol.|pages=525–9 | last1 = Milroy | first1 = CM | last2 = Clark | first2 = JC | last3 = Carter | first3 = N | last4 = Rutty | first4 = G | last5 = Rooney | first5 = N | doi=10.1136/jcp.51.7.525}}</ref>

For reason of safety and security a rule of use of the [[Gun safety#Safety flag|safety flag]] has been strictly mentioned by ISSF for the 10m air pistol and rifle shooting sports events.

== See also ==
* [[Blowgun]]
* [[Marksmanship]]
* [[Airsoft]]
* [[Paintball]]

==References==
{{Reflist}}
----
*[https://www.britannica.com/technology/air-gun Air gun | BB gun, Pellet Gun, Airsoft | Britannica]

==External links==
{{commons category}}
* [https://www.pyramydair.com/blog/a-history-of-airguns/ Tom Gaylord's History of Airguns]

{{Hunting topics}}
{{Authority control}}

{{DEFAULTSORT:Air Gun}}
[[Category:Air guns| ]]
[[Category:Hunting equipment]]
[[Category:Pneumatic weapons]]
[[Category:Swedish inventions]]
[[Category:Rifles]]
[[Category:Pistols]]