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Modern air guns are typically low-powered for safety concerns, but high-powered designs have been used for hunting and military applications. They do benefit from very high accuracy, and are used in sharpshooting events in the Olympic Games.

Most airguns can be practiced in a backyard or garden, and even indoors with the proper backstop. Some of the stronger power "springers" can propel a pellet beyond 1100 ft/s (340 m/s) at approximately the speed of sound. It will produce a noise similar to a .22 cal (~5.5 mm) rimfire. These pneumatic rifles can be found in the following calibers, .177 (~4.5 mm) most common, .20 (~5.0 mm) Benjamin Sheridan, .22 (~5.5 mm) most common for hunting, .25 (~6.4 mm), 9 mm and even .50 (~12.7 mm).

Contents 1 Powerplant technology 1.1 Multi-stroke pneumatic airguns 1.2 Spring-piston guns 1.3 Gas piston guns 2 Ammunition 2.1 Cylinder guns 2.2 Precharged pneumatic airguns 2.3 Reservoir guns 3 Choosing an airgun 4 History 5 See also 6 External links

Powerplant technology

There are many different types of air guns in terms of powerplants that are used to get the air moving: spring-piston, multi-pump (multi-stroke) pneumatic, single-stroke pneumatic, precharged pneumatic (PCP), and reservoir. All of them have advantages and disadvantages.

Multi-stroke pneumatic airguns

They require 2-10 pump-ups of an on-board lever to store compressed air in the powerplant. Variable power can be achieved through this process, as the user can input more power for pellets for long-range target practice, or input less for BBs or shorter-range shots. In the United States, the Crosman Corporation is the predominant manufacturer of pump-up rifles and pistols.

Spring-piston guns

Spring-piston air guns are able to achieve muzzle velocities near the speed of sound from a single stroke of a cocking lever or the barrel itself. The difficulty of the cocking stroke is usually related to the power of the gun, with higher muzzle velocities requiring greater cocking effort.

Spring-piston guns operate by means of a spring-loaded piston in a chamber separate from the barrel. Cocking the gun compresses the spring; pulling the trigger releases it and causes the piston to compress air in the chamber directly behind the pellet. The spring is usually made in the form of a steel coil.

As the air compresses, it becomes very hot (Charles' Law), often in excess of 1000 °C. Because of the rapidity of the firing process, very little of this heat is lost into the gun's metal parts. Consequently, spring-piston guns are more efficient than reservoir guns. Lubricants (such as molybdenum disulfide) are generally designed so that they burn gently at this temperature; upwards of 30% of the energy of the shot may come from this effect. On the other hand, excessively flammable lubricants may detonate and damage the gun.

Spring-piston guns seem to have a practical upper limit of 1200 ft/s (370 m/s) for .177 cal (4.5 mm) pellets. Higher velocities cause unstable pellet flight and loss of accuracy.

Most spring piston guns are single shot breech loaders by nature (somewhat like an old shotgun) but multiple-shot guns have been increasingly common in recent years. Spring guns are typically cocked by a mechanism is which the gun is hinged at the mid-point, with the barrel serving as a cocking lever. Other systems used include side levers, under-barrel levers and motorized cocking, powered by a rechargeable battery.

Unlike cartridge firearms, the spring is very powerful in these guns and is held back by a sear that has a very small engagement area. There have been cases of severe crushing and even amputation when the spring has been released unexpectedly. Always use one hand to restrain the cocking lever when loading these guns so that should the sear slip, you will not be injured.

Spring guns, especially the higher powered ones, have a tendency vibrate/recoil quite a bit. Although this recoil is not comparable in magnitude to that of a cartridge firearm, it can make the gun difficult to shoot accurately as the vibration is well under way while the pellet is still in the barrel. Most guns seem to respond well to a light repeatable hold that allows the gun to vibrate the same way from shot to shot. Spring gun recoil also has a sharp forward component, caused by the piston as it hits the forward end of the chamber when the spring behind it reaches full expansion. This sudden forward acceleration is hardly felt by the user, since the backward and forward recoil forces happen within milliseconds of each other, but it is infamous for breaking telescopic sights used on regular firearms. On any but the lowest power spring guns, any mounted telescope should be airgun rated. Spring gun tuning can reduce vibration to very low levels. Airgunsmiths specialize in airgun modifications.

The better quality spring air guns can have long service lives, often exceeding thirty years. Because they deliver the same energy on each shot, the trajectory is extremely repeatable. This repeatability resulted in most Olympic air gun matches through the 1970s and into the 1980s being shot with spring-piston guns. Beginning in the 1980s, guns powered by compressed, liquefied carbon dioxide began to dominate competition. Today, the guns used at the highest levels of competition are powered by compressed air stored at very high pressures of 2000 to 3000 lbf/in² (14 to 21 MPa).

The Chinese army uses spring-piston small arms to train more economically. Surplus military-issue Chinese spring-piston air-guns are sometimes available by mail-order.

Gas piston guns

Some more expensive models use a "gas piston": pressurized air is held in a special chamber built into the piston, and this air is pressurized when the piston is cocked. Gas piston guns require higher precision to build, since they require low friction sliding seal that can withstand the high pressures when cocked. The advantages of gas pistons include the ability to vary the power of the gun by changing the amount of air in the gas piston, the reduction in moving mass during firing (and a corresponding reduction in felt "recoil" caused by the piston and spring starting and stopping), and elimination of the problems of spring fatigue. A notable disadvantage should be the loss of energy as dissipated heat.

One specialized adaptation is the light gas gun, which usually uses a gunpowder propelled plastic piston compressing a cylinder full of hydrogen gas. Light gas guns are capable of accelerating a 5 mm projectile to a velocity of 6000 m/s in a distance of about a meter.

Ammunition

The typical projectile used in rifled airguns is the lead diabolo pellet. This is a wasp-waisted projectile open at the base and having a variety of head styles. The diabolo pellet is designed to be drag stabilized. This, in addition to the spin afforded by the rifling, makes the airgun one of the most accurate of all guns. Another advantage of the diabolo pellet is that the high drag produces short maximum ranges which adds to safety. The diabolo pellet is not as stable as some other shapes in the transonic region. While some high power spring guns can propel light pellets at or beyond the speed of sound, this results in decreased accuracy and often decreased life of the spring and seals (the low momentum of the light pellet causing it to start moving down the barrel before maximum pressure is reached resulting in loss of the air cushion and subsequent slamming of the piston/seal into the end of the chamber at high velocity.)

Most air guns have a calibre of .177 (4.5 mm), and are designed for target practice. Cost per round is less than $0.02 (US) for Olympic-quality ammunition, and far less for cheaper grades. .20 .22 and .25 calibre (~5.1, ~5.6 and ~6.4 mm) guns exist, and are used mainly for hunting and field target shooting. Other Air Guns use a BB. A BB is a small metal ball usually made out copper coated steel. Typically on the market today the standard BB is in .177 (4.5mm)caliber designed to be fired from beginner and intermediate-level airguns. They can produce a higher muzzle velocity than a pellet at the same caliber. However, because of the sphere-shape of the BB (as opposed to a more conical pellet shape), downrange accuracy is lost, as the BB starts to tumble out of control at longer ranges. Typically BBs are used for practice indoors or for airgun enthusiasts who like to do target practice, but can not afford a high-power pellet or higher-power airgun systems.

Cylinder guns

Cylinder guns shoot from a purchased cylinder, usually filled with liquefied carbon dioxide. Most paintball guns are this type. There are also CO₂ charged airguns that are very popular for plinking. Carbon dioxide powered guns have one significant advantage over true air guns, that of the liquid carbon dioxide maintaining a constant vapour pressure in the reservoir while there is still liquid present. Thus, many shots are available between recharging and good consistency of velocity is maintained over a long period of time. Some CO₂ powered target guns have detachable or fixed reservoirs that are loaded with liquid gas from a larger cylinder, often of the type used to power home-brew kegs.

Newer airguns on the market uses the CO₂ cylinder to great effect. With the advent of the smaller12 gram CO₂ cylinder, airguns are currently shifting towards using this new technology. One major advantage for CO₂ cylinder airguns is the ability to have semi-automatic and full-automatic fire. Another advantage is the inter-changeability and ease of use of the 12 gram CO₂ cartridge. The advantages of smaller and more cost-effective CO₂ cartridges allow many airgun manufacturers to switch from other airgun types to CO₂.

Commonly on the market today, you would see most air-pistols equipped with the 12gram CO₂ cylinder system in .177(~4.5mm), .20(~5.0mm), .22(~5.5mm), and even .25 (~6.0mm). Capable of semi-automatic fire, these appeal most to beginner and intermediate pistol shooters who don't want to have a fuss with the common powder cartridges.

Other rifles with the CO₂ system on the market would be the traditional bolt-action rifles. Through performance enhancements, bolt-action CO₂ rifles can have a muzzle velocity of 600+ feet/s.

There are a certain number of semi-automatic air-rifles with the CO₂ cylinder power system on the market, such as the Crosman 1077, designed with a 12-shot .177 (~4.5) magazine. Air-rifles of this type are popular with beginners and intermediates, who like to have fun plinking or targe practice, but don't want the hassle of dealing with charging the tank, or dealing with pumping a pneumatic airgun.

Lastly, the CO₂ system have been used in experimental non-lethal law enforcement weapons, where high power delivery systems launch rubber batons or bean bags out of a gas grenade-like launcher, much like a non-lethal shotgun system (but at lower velocities, thus being safer).

Precharged pneumatic airguns

PCP (pre-charged pneumatic) airguns can be used for hunting and competition. These are usually filled from an air reservoir, such as a diving cylinder.

See also Airsoft.

Reservoir guns

Reservoir guns, sometimes called "multi-pump" guns, have a pump to compress air into a reservoir. Most of these gun require multpile pumps to fire a single shot, therefore have lower rate of fire when compared to other types of air rifles. Most reservoir guns use the same ammunition as spring-piston guns.

Most historical air-guns were reservoir guns. The air gun carried by Lewis and Clark was a reservoir gun.

Many reservoir guns have been used for hunting. One of the traditional weapons for hunting wolves in Russia was said to be a large-calibre reservoir air-rifle. It is said to have shot silently to avoid warning the pack. Modern reservoir guns in larger calibers (6 to 9 mm) are often used for hunting small game.

The multi-pump and CO₂ pneumatics have been popular in the United States, where they are known as "BB guns" or "pellet guns," depending upon the type of projectile used. These are typically viewed in other countries as children's toys. There are exceptions to this, as companies such as Benjamin Sheridan, Crosman, and Daisy market sophisticated systems (though Daisy and Crosman, also manufacture children's guns).

Pneumatic reservoir guns have one advantage over the other types of air-rifles: Its sustainability and ruggedness. Most other designs are fairly complex, and require higher maintenance to keep the airgun operating. Pneumatic airguns have looser tolerances, and because of its simplicity, requires marginal maintenance to keep it functioning. Pneumatic airguns also are cheaper to produce and to buy off the market, as their components do not require much special manufacturing methods.

For most beginners and intermediates, multi-pump pneumatic reservoir air-guns and air-rifles have been the cost effective choice. The design of higher quality and match-grade multi-pump air rifles can propel a pellet to excess speeds of 700-800 feet/second. Without the need to purchase an additional powersource, the cost-effective pneumatic airguns and air rifles have been gaining popularity in the U.S. and worldwide.

Choosing an airgun

• Self-contained: spring-piston, multi-stroke pneumatic, single-stroke pneumatic. These guns require no additional CO₂ cylinders, and are thus cheaper to operate.
• Noise Level: spring-piston. Absence of loud gas discharges makes these guns quieter to operate. Consider when practicing in cramped urban areas.
• Accuracy: pre-charged, single-stroke pneumatic. Without the variable factor introduced by CO₂ cylinders or the recoil introduced by the spring, the mechanisms in these guns have more repeatable shots.
• Convenience: pre-charged or CO₂ powered. These guns don't require constant cocking, and are hence more popular with recreational shooters.

The above points are generalizations. The overall performance of your airgun will depend on its quality. For instance, a match-grade CO₂ rifle will have better accuracy than a cheaper spring-piston import. The extra cost translates into greater quality, accuracy, shot-placement, etc.

When choosing an air rifle or an air pistol consider where (club range, backyard, condo, farm) and how (competition, target practice, plinking, pest-control) you plan to use it.

History

Reservoir guns represent the oldest pneumatic technology; they have existed since the 15th century. They presented some compelling advantages over the primitive firearms of the day. These airguns could be fired in wet weather (unlike flintlocks), and with greater rapidity than the muzzle-loading guns of the period. Moreover, they were more quiet, had no muzzle flash, and did not produce telltale clouds of smoke.

Contrary to popular myth, a military-grade airgun is not "silent". It makes a very audible sound, but less than a modern pistol. One may safely assume that it was practically silent against the noise of a pitched battle.

For general usage, though, airguns were no real challenge to the dominant position of powder weapons. They were expensive, delicate and not very powerful. The air reservoirs could burst explosively. The valves were not very tight and slowly leaked pressure. Historical accounts mention that the common soldiers were often unable to handle the complex guns, which was logical in an age where the average peasant recruit had never encountered a machine more complex than a horse-drawn cart. People who had any experience with mechanical devices (millers or clockmakers) were few and far between. The guns of the period were famously crude, and required very little skill from the average infantryman (skilled snipers or hunters were something else entirely, see Jäger).

In this era, France, Austria and other nations had special detachments of snipers who carried air-rifles.

The Austrian 1780 model was named "Windbüchse" (literally "wind rifle") in German. The guns were developed by the gunsmith Bartholomeo Girandoni (1744-1799), and are occasionally called "Girandoni air guns" in literature (the name is occasionally spelled "Girandony"). The Windbüchse was about 4 ft (1.2 m) long and weighed 10 pounds (4.5 kg), which was about the same size and mass as a conventional musket of the time. The reservoir was a removable, club-shaped butt; the gun was recharged by replacing the exhausted reservoir with a new one. The Windbüchse carried twenty lead balls of .52 inch caliber (13mm) in a tubular magazine. It could shoot one magazine in about thirty seconds, which was a fearsome rate of fire compared to the slow-loading muzzle loaders of the period. A shot from this gun could penetrate a one-inch wooden board at a 100 paces. The effect is roughly equal to that of a modern 9 mm or .45 inch pistol.

The celebrated expedition headed by Lewis and Clark reportedly carried a large-caliber reservoir gun.

Some of the largest pneumatic guns in history were mounted on the USS Vesuvius. This naval vessel was armed with three 15 inch (381 mm) reservoir-powered cannons that fired highly explosive projectiles. Unfortunately for the future of airguns, these suffered from poor range and, unlike conventional cannon, could not rotate relative to the rest of the ship.

See also

• Marksmanship
• Airsoft
• BB gun

External links

• The UK Air Gun Forum
• American Airguns Web Page
• Airgun.org
• Canadian airgun forum
• UK Airgun website
• SpeedyToys, vendors of airsoft guns
• Girandoni style air rifles and pistols - preliminary research presentation, an article by Robert D. Beeman Ph.D., with many photographs.

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