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== 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 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 β 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 β the barrel is fixed to the receiver, and the cocking is done with a separate cocking lever ** Underlever β the cocking lever is located underneath the barrel or the receiver and is flexed downwards during cocking ** Sidelever β the cocking lever is located to the side (usually the right side) of the receiver and is flexed sideways during cocking ** Overlever β 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 β ''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 β 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>[https://www.researchgate.net/publication/326191398_Internal_Ballistics_of_PCP_Airguns Internal Ballistics of PCP Airguns by Domingo Tavella, August 16, 2018]</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 β 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=http://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.
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