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Special Investigation: Airguns

Updated: Aug 20, 2019


Our second special investigation focuses on the Air Gun market. We give you all the important information from around the globe to help you grow your export business.


An airgun is any kind of gun that launches projectiles pneumatically with compressed air or other gases that are pressurized mechanically without involving any chemical reactions, in contrast to a firearm, which pressurizes gases chemically via an exothermic oxidation (deflagration) of combustible propellants which generates propulsive energy by breaking molecular bonds. Both the long gun and handgun forms (air rifle and air pistol) typically propel metallic projectiles, that are either diabolo-shaped pellets, or spherical shots called BBs. Certain types of air guns (usually rifles) may also propel darts or arrows.

The first air guns were developed as early as the 1500s. They have been used in hunting, sporting and warfare. Modern air guns use one of three types of power source depending on the design: spring-piston, pneumatic, and bottled compressed gas (most commonly carbon dioxide).


History

Air guns indicate the oldest pneumatic technology. The oldest surviving mechanical air gun, a bellows air gun dating back to approximately 1580, is in the Livrustkammaren Museum in Stockholm. This is the time most historians identify as the beginning of the modern air gun.

Throughout 17th to 19th century, air guns in calibers .30–.51, were used to hunt big-game deer and wild boar. These air rifles were charged using a pump to fill an air reservoir and gave velocities from 650 to 1,000 feet per second (200–300 m/s). They were also used in warfare, the most recognized example being the Girandoni air rifle.

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. Their first model air gun was the wooden Challenger and marketed in 1886. In response, Clarence Hamilton from the neighbouring 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 catalogue. 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 all together in the 1940s.

During the 1890s, air rifles were used in Birmingham, England, for competitive target shooting. Matches were held in public houses, which sponsored shooting teams. Prizes, such as a leg of mutton for the winning team, were paid for by the losing team. The sport became so popular that in 1899, the National Smallbore Rifle Association was created. During this time over 4,000 air rifle clubs and associations existed across Great Britain, many of them in Birmingham. During this time, the air gun was associated with poaching because it could deliver a shot without a significant report.


Use

Air guns are used for hunting, pest control, recreational shooting (commonly known as plinking), and competitive sports, such as the Olympic 10 m Air Rifle and 10 m Air Pistol events. Field Target (FT) is a competitive form of target shooting in which the targets are knock-down metal silhouettes of animals, with a 'kill zone' cut out of the steel plate. 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 7.3 and 41.1 metres (24 and 135 ft) for HFT & 7.3 and 50.29 metres (24.0 and 165.0 ft) 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. 12 ft⋅lbf (16 J).

The increasing affordability of higher-power 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 .35 inches (8.9 mm) and targets at 75 and 100 yards (69 and 91 m), while the Big Bore Benchrest arm of the same competition engages targets at 35 to 300 yards (32 to 274 m).



Propellant

The different methods of powering an air gun can be broadly divided into three groups: spring-piston, pneumatic, and compressed CO2. These methods are used in both air rifles and air pistols.


Spring-piston

Spring-piston air guns (or simply "spring guns" or "springers") operate by means of a spring-loaded piston pump assembly contained within a compression chamber separate from the gun barrel. Traditionally, a grease-lubricated steel coil spring is used as the powerplant main spring. Before shooting, the user need to manually cock the gun by flexing a lever connected to the pump assembly, which drives the pump piston rearwards and compress the main spring until the rear of the piston engages the sear. The act of pulling the trigger disengages the sear, allows the spring to decompress and release the elastic potential energy stored within it, and pushes 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 sitting in the barrel chamber, once the air pressure has risen enough to overcome any 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 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 ignited by the compression heat like in a diesel engine, and lead to an afterburner effect with (often unpredictable) additional thrusts, as well as combustion smoke coming out of the muzzle upon firing. Most spring-piston guns are single-shot breechloaders by nature, but multiple-shot repeaters with magazine feeders have become more common in recent years.

Spring-piston guns, especially the high-powered "magnum" guns, are able to achieve muzzle velocities near or exceeding the speed of sound. The effort required for the cocking stroke is usually related 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 1,250 ft/s (380 m/s) 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 rapidly as pellets are pushed past the speed of sound, so it is generally better to increase pellet weight to keep velocities subsonic in high-powered guns. Sonic crack from the pellet as it moves with supersonic speed also makes the shot louder sometimes making it possible to be mistaken for firearm discharge. Many shooters have found that velocities in the 800–900 ft/s (240–270 m/s) range offer an ideal balance between power and pellet stability.


Gas spring

Some newer generation of 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. When the gun is cocked, the gas inside the cylinder gets further compressed by the piston, stores potential energy and acts in effect as a pneumatic 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, smoother recoil pattern and faster "lock time" (the time between pulling the trigger and the pellet being discharged) which results in better accuracy. Gas springs perform more reliably in cold climates, as the grease used to lubricate coil springs often overthicken in low temperatures, causing the gun to "freeze up". Gas springs also have less lateral vibrations than coil springs, hence are usually less "hold-sensitive" and hence easier to achieve consistent shot groupings.


Pneumatic

Pneumatic air guns propel the projectiles by utilizing the 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 pump to pressurize air in an internal reservoir, while pre-charged pneumatic guns' reservoirs are filled from an external source using either a high-pressure hand pump or by decanting air from a diving cylinder.


Pump pneumatic

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

In single-stroke pneumatic air guns, 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 ISSF 10 metre air rifle shooting events from the 1970s up to the 1990s.

Multi-stroke pneumatic air guns use multiple pumpings to achieve variable power levels in order to adapt for both long or short-range shooting. This air gun are usually single-shot, which each shot requires approximately 5 strokes. However, up to five shots are possible, usually requiring around 10 to 20 strokes as long as the air reservoir is enough to store higher pressure. For safety reasons, most multi-stroke guns are usually designed to have its pump lever jammed when the reservoir has reached its maximum pressure limit, which 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

Pre-charged pneumatic (PCP) air guns have their internal reservoir pre-filled from an external air source (such as a diving cylinder, or by charging with a hand pump), and remains pressurized until depleted after repeated shooting. UK-based company Daystate has been credited as the airgunmaker who founded modern-day precharged pneumatic (PCP) air rifles.

During shooting, the hammer strikes the reservior'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 regulator valve). 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 the UK and Europe because of their accuracy and ease of use. They are widely utilized in ISSF 10 metre air pistol and rifle shooting events, the sport of Field Target shooting, and are usually fitted with telescopic sights.

Early hand-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 hand pumps have built-in air filtration systems and have overcome many of these problems. Using scuba-quality air decanted from a scuba 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 ). A well-designed PCP will display good shot-to-shot consistency over longer 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

Originally called CG guns (compressed gas guns), air guns utilizing prefilled removable gas cylinders as power source have now become known as CO2 guns due to the ubiquitous commercial use of bottled carbon dioxide gas. Most CO2 guns use a disposable cylinder called a "Powerlet", that is often purchased with 12 grams (0.42 oz) of pressurized CO2 gas, although some, usually more expensive models, use larger refillable CO2 reservoirs like those typically used with paintball markers.

CO2 guns, like other pneumatic guns using compressed air, offer power for repeated shots in a compact package without the need for complex cocking 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 CO2 power. These 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.





Ammunition


Pellet

The most popular ammunition used in rifled air guns is the wasp-waisted 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 rear portion called the "skirt", which expands and fully engages the bore to provide a good seal, thus allows maximal efficiency in pellet propulsion during shooting. In flight, the skirt has greater drag-to-weight ratio than the head, and provides drag-stabilization similar to that of a shuttlecock. This shape design also means that the overall pellet will have poor ballistic coefficient and tends to be more unstable than some other projectile shapes, especially in the transonic region (272–408 m/s ~ 893–1340 ft/s). Diabolo pellets are traditionally made from lead, but can also be manufactured from tin, or a combination of materials such as steel or gold alloys with polymer tips.


Slug

Some manufacturers also have recently introduced the more cylindrical-shaped "slug" pellets for the more powerful modern PCP air rifles. Compared to the commonly used diabolo pellets, these slug pellets resemble Minié balls and have more contact surface with the bore and hence needs greater propelling force to overcome friction, but have better aerodynamics and longer effective ranges due to the more similar shape to firearm bullets, however also require a fully rifled barrel for spin stabilization in flight.




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