Air gun

Umarex CPSport air gun (copy of Walther P99). Unlike traditional pistols, the magazine is inserted into a slot in the middle of the slide (left open in picture), while the CO2 capsule goes into the grip (left halfway out in picture). The red dot visible on the frame indicates that the safety is off.

An air gun is a pneumatic gun which fires projectiles using compressed air or other high pressure gas as a propellant.

Legal issues

The legal definition of an airgun differs from country to country; in the United Kingdom, for example, air pistols generating more than 6 foot pounds or air rifles generating more than 12 foot pounds of energy are considered firearms, as are airguns in Canada with a muzzle velocity of over 500 f/s (152.4 m/s). In Japan, any airgun that fires a metallic projectile is restricted as a firearm, so only airsoft type guns are readily available there. Many US cities and states restrict airgun sales and possession, usually independent of the power; these include: New York City, New York, New Jersey, Michigan, Chicago and Morton's Grove Illinois, San Francisco California, or Philadelphia Pennsylvania[1].

Even airguns not considered firearms are subject to regulation in most areas; at the very least they will be considered dangerous or deadly weapon. There are minimum ages for possession, usually less than the age for firearms. Sales of both airguns and ammunition may be restricted as well. Some areas may require permits and background checks similar to those required for firearms possession. In the UK, there is currently a move to ban Brocock Air Cartrdige System airguns, which use a precompressed, single shot air cartridge similar in size of a .38 Special catridge. A number of these have been modified by criminals to convert them to make zip guns capable of firing rimfire ammunition or even .38 Special ammunition[2].

Use

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), approximately the speed of sound. These will produce a noise similar to a .22 cal (5.5 mm) rimfire, while most other airguns are significantly quieter. Airguns are most commonly found in the following bore diameters:
*.177 inches (4.5 mm), the most common, used in Olympic events
*.20 inches (5.0 mm), found in some Eurpoean and all American Sheridan airguns
*.22 inches (5.5 mm), the most common for hunting
*.25 inches (6.4 mm), the largest commonly available bore.

Larger bores do exist; a Korean maker sells air rifles in 9 mm (.355 inch) and larger bores. Custom makers regularly produce air rifles in common muzzleloading rifle calibers, such as .45 (11.5 mm), .50 (12.7 mm), .58 (14.7 mm) and even larger. These large bore airguns, by makers such as Gary Barnes, are usually very expensive, handmade items, suitable for hunting medium sized game.

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, several makes are available for multi-stroke airguns including: Benjamin, Daisy, Crosman, Gamo and others.

Single-stroke pneumatic airguns

As the name implies, one motion of the cocking lever is all that is needed to compress the air for propulsion. At first glance, this design would seem to offer lower power than multi-stroke airguns. However, most single-stroke airguns use a spring type power plant. When the airgun is cocked, a large spring is compressed which, when the trigger is pulled, compresses the gas (air) at the time of firing. These airguns are called "mainspring airguns" in most literature. Usually, it is this category of airgun that presents the highest muzzle velocity, power, and accuracy.

Early match-grade mainspring guns included the RWS 75T series and the Feinwerkbau 4301 and 300S, both of these airguns utilized a mainspring design with opposed air pistons for reduction in the airgun's recoil at time of firing. Later models, exemplified by the world standand non-precharge design Feinwerkbau 603, use a single "pump" of a secondary sealed gas chamber. It is a chamber of gas, not a spring, that when compressed serves as the potential energy storage for the eventual discharge of the pellet. This airgun design, of all of the mechanical spring airguns (sometimes called a 'gas spring airgun') is the epitome of design elegance. When properly designed, it exhibits extremely high power. Alternately, design compromises may be made resulting in the highest accuracy of any ballastic arm, airguns and firearms included.

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.

An older single shot spring-piston air gun.

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 is compressed it increases in temperature (Charles' Law) becoming very hot, possibly 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 (see adiabatic process). Consequently, spring-piston guns are more efficient than reservoir guns.

Modern air gun lubricants (such as molybdenum disulfide) are generally designed so that they do not burn at this temperature. Before the availability of synthetic lubricants, when petroleum based products were used, upwards of 30% of the energy of the shot may have come from the burning or "dieseling" of some of the lubricant, according to some writers. The use of such combustible lubricants in modern guns, which are much more highly stressed, can severely damage the spring and piston seals.

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. 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.

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 requiring the gun to be hinged at the mid-point (called a break barrel), with the barrel serving as a cocking lever. Other systems that are used include side levers, under-barrel levers, and motorized cocking, powered by a rechargeable battery.

The spring in a spring piston air gun is very powerful 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. Spring piston shooters should always use one hand to restrain the cocking lever when loading these guns so that should the sear slip, they will not be injured.

Spring guns, especially the higher powered ones, have a significant recoil resulting from the forward motion of the piston. Although this recoil is less than that of a cartridge firearm, it can make the gun difficult to shoot accurately as the recoil forces are well under way while the pellet is still traveling down the barrel. Most guns seem to respond well to a light, repeatable grip 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 helps to counteract the backward recoil, since the backward and forward recoil forces happen within milliseconds of each other, but it is infamous for knocking around and loosening the lenses and reticles found in telescopic sights, even those which are designed to withstand the (backward-only) recoil from high-powered firearms. On any but the lowest power spring guns, any mounted telescope should be airgun-rated.

Spring guns can also suffer from spring vibrations that upset accuracy. These vibrations can be controlled by adding features designed into the gun, like close-fitting spring guides, or by aftermarket tuning done by airgunsmiths who specialize in airgun modifications. A common modification is the addition of viscous silicone grease to the spring, which both lubricates it and damps out vibration.

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. These military-issue Chinese spring-piston air-guns are often available by mail-order, but the buyer should note that quality control on these guns tends to be somewhat variable.

Gas piston guns

Some more expensive models (pioneered by the Theoben company in the UK) use a "gas ram"; pressurized air or nitrogen is held in a special chamber built into the piston, and this air is further pressurized when the gun is cocked. It is in effect a gas spring. Gas ram guns require higher precision to build, since they require a low friction sliding seal that can withstand the high pressures when cocked. The advantages of the gas ram include the ability to vary the power of the gun by changing the amount of air in the ram, the reduction in moving mass during firing (and a corresponding reduction in felt "recoil" caused by the piston and spring starting and stopping), a faster lock time compared to ordinary spring guns, and elimination of the problems of spring fatigue. A possible disadvantage is the 'snappy' firing cycle when compared to the slightly slower motion of a conventional spring. This was true on earlier guns of the 1980s but later developments included the use of a floating inertia weight which helped to soften the recoil. A subsequent development is the 'gas strut'. This is an aftermarket fitment that takes the place of the mainspring and guide in many conventional airguns and turns them into gas ram rifles.

One specialized though unconnected adaptation of the principle 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.

CO₂ guns

Most CO₂ guns use a disposable cylinder that is purchased prefilled with liquefied carbon dioxide. (Some paintball guns are this type, although most use refillable CO₂ resevoirs.) Carbon dioxide powered guns have one significant advantage over precharged pneumatic air guns: So long as some liquid CO₂ remains in the reservoir, a constant vapour pressure results in constant velocity over a wide range of ambient temperatures without the need for a pressure regulator. This allows CO₂ guns to be constructed more simply than guns used a pressurized air reservoir. Some CO₂ powered guns have detachable or fixed reservoirs that are loaded with liquid gas from a larger cylinder. Most CO₂ powered guns use the standard 12 gram disposable cylinder. Recently Crosman has introduced a new 88 gram cylinder that is used in some of their guns; it has yet to receive wide use by other manufacturers.

CO₂ guns, like compressed air guns, 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 a great many replica revolver and semiautomatic pistols designs on the market that use CO₂ power. These guns are popular for training, as the guns and ammunition are inexpensive, 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, although there are still a few precision target guns on the market that use CO₂.

Lastly, the CO₂ system has 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. Because of the need for cylinders/charging systems PCP guns have higher initial costs but very low operating costs compared to CO₂ guns. These guns are often used for hunting purposes in other countries (than the U.S.) because of restrictive firearm laws. PCP guns have very low recoil and can fire many shots (from fewer than 30, to as many as 500 [3]) from one filling, and because of the ready supply of gas are ideal for repeating mechanisms. Several manufacturers produce repeating PCP guns, usually with rotary magazines of 8 - 16 shot capacity.PCP guns are very popular in the UK and Europe due to their accuracy and ease of shooting. They are widely utilised in the sport of Field Target shooting, [4] fitted with high magnification optical scopes for accurate rangefinding. [5]There is currently a craze in the U. S. for big-bore pre-charged pneumatic air rifles. Many of these, such as the .45,.50 and .68 calibre paintballs (see paintball for more) are expensive but are among the most powerful air guns manufactured. 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 multiple 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 rifles 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, though such guns are actually surprisingly loud. Modern reservoir guns in larger calibers (6 to 9 mm) are often used for hunting small game in the U.S.

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 advantages over the other types of air-rifles: 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 per second. Without the need to purchase an additional power source, the cost-effective pneumatic airguns and air rifles have been gaining popularity in the U.S. and worldwide.

Ammunition

.177 caliber ammunition next to a stick of gum.

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 collision 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.

Probably the most common air gun ammuition in the USA is the BB. A BB is a small steel ball usually made of copper- or zinc-coated steel. The name "BB" comes from the BB-size lead shotgun pellet, which meaures a nominal 0.180", but modern BBs actually measure approximately 0.171"-0.173". BBs can be very accurate at short distances when fired from properly designed guns. The Daisy Model 499 was specifically designed for target competition at 15' using precision-ground BBs. However, because BBs are not fired from rifled barrels, as are pellets, they lack the spin stability that gives pellets long-range accuracy. As a consequence, BB accuracy is questionable at longer ranges. Typically BBs are used for practice indoors, for casual outdoor plinking, for training children, or for airgun enthusiasts who like to do target practice, but cannot afford a high-power pellet or higher-power airgun systems.

Some shotgunners use sightless BB rifles to train in instinctive shooting. Similar guns were also used briefly by the United States Army in the 1960s as part of an instinctive shooting program termed "Quick Kill."

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 and vice-versa. 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 quieter, 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, though much quieter than a 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 9mm or .45 caliber pistol.

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

During the 1890s, air rifles were used in Birmingham, England as a competitive target sport. Shooting matches often took place between enthusiasts; one public house would sometimes challenge another with prizes such as a leg of mutton for the winners which was paid for by the losers. The sport became so popular in the city that just after the turn of the century the National Air Rifle Association was set up in the city; during this time over 4000 air rifle clubs and associations existed across Britain, many of them in Birmingham.

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 dynamite guns suffered from poor range and, unlike conventional cannon, could not rotate relative to the rest of the ship.

See also

* Marksmanship
* Airsoft
* BB gun
* Gun Quarter
* Anschütz
* Feinwerkbau

References

* History of Air guns

External links

* British airgun forum
* Airsoft Airgun Reviews
* History and Early Origins of the air rifle
* The UK Air Gun Forum
* United Kingdom Association for Hunter Field Target
* Airsoft Safety Precautions safety rules and more.
* American Airguns Web Page
* Airgun.org
* Canadian airgun forum
* Girandoni style air rifles and pistols and preliminary research presentation
* International Shooting Sport Federation
* Gary Barnes 87 calber (22 mm) smoothbore airgun