How Does A Pneumatic Air Rifle Work

[Violet Mcdow]

Anair gun or airgun is a gun that uses energy from compressed air or other gases that are mechanically pressurized and then released to propel and accelerate projectiles, similar to the principle of the primitive blowgun. This is in contrast to a firearm, which shoots projectiles using energy generated via exothermic combustion (deflagration) of chemical propellants, most often black powder or smokeless powder.

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 pellets or spherical shots called BBs, although in recent years Mini ball-shaped cylindro-conoidal projectiles called slugs are gaining more popularity. Certain types of air guns (usually air rifles) may also launch fin-stabilized projectile such as darts (e.g., tranquilizer guns) or hollow-shaft arrows (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-piston, pneumatic or bottled compressed gas (most commonly carbon dioxide and recently nitrogen).

Air guns represent the oldest pneumatic technology. The oldest existing mechanical air gun dates back to about 1580, and is 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 calibers 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 ft/s (200 to 300 m/s). They were also used in warfare, the most recognized example being the Girandoni air rifle.

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 muskets), and discharged much faster than muzzle-loading guns.[1] Moreover, they were quieter than a firearm of a similar caliber, had no muzzle flash, and were smokeless. Thus, they did not disclose the shooter's position or obscure the shooter's view, unlike the black powder muskets of the 18th and 19th centuries.

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 Dutch in Dejima.

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 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,[5] 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 target shooting.[6] Matches were held in public houses and working men's clubs, 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.[7] Prizes, such as a leg of 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.[6] During this time, the air gun was associated with poaching because it could deliver a shot without a significant muzzle report.[citation needed]

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 .30 inches (7.6 mm) at 75 yd (68.58 m) while the Big Bore Benchrest arm of the same competition at other localities engages targets at 35 to 300 yards (32 to 274 m).

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 CO2), which uses external sources of pressurized gas.[10]

A spring-piston air gun (also known as a spring gun or simply a "springer") operates 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 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. When shooting, the 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, 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 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. This often results in combustion smoke coming out of the muzzle and potential pressure damage to the rubber O-ring seals 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 breechloaders by nature, but multiple-shot repeaters with magazine feeders have been introduced in recent years by manufacturers such as Gamo, Umarex and Hatsan.

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, 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 scopes not rated for spring gun usage. In addition, the spring often has unpredictable collateral transverse vibrations as well as 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] Most Olympic 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.

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. 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. 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, 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 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 groupings.

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