Shooting

Air guns represent the oldest pneumatic technology. The oldest existing mechanical air gun, a bellows air gun dating back to about 1580, is in the Livrustkammaren Museum in Stockholm. This is the timeline most historians peg as the beginning of the modern air gun.

In the 17th 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 650-1,000 feet per second. They were also used in warfare; the most famous example is the Girandoni Air Rifle.

At that time, they had compelling advantages over the primitive firearms of the day. For example, air guns could be fired in wet weather and rain (unlike matchlock muskets) and with greater rapidity than muzzle-loading guns. Moreover, they were quieter than a firearm of similar caliber, had no muzzle flash, and were completely smokeless, thus not disclosing the shooter's position or obscuring his view. Black powder muskets of the 18th and 19th century produced huge volumes of dense smoke when fired, a disadvantage compared to air rifles.

Although some enthusiasts talk about air guns posing a serious alternative to powder weapons, that was never proved to be the case, as valve leaks and bursting reservoirs were known problems. Air guns also were delicate and crude, and peasant-soldiers, many of whom had never seen any mechanical tools more complex than horse-drawn carriages, could not have operated or maintained them properly.[citation needed] Later improvements in valve designs and reservoir strength either came too late or were too complex for the few air gunsmiths of the day.

But in the hands of skilled soldiers, they gave the military a distinct advantage. France, Austria and other nations had special sniper detachments using air rifles. The Austrian 1780 model was named Windbüchse (literally "wind rifle" in German). The gun was developed in 1778 or 1779 [1] by the Tyrolese watchmaker, mechanic and gunsmith Bartholomäus Girandoni (1744–1799) and is sometimes referred to as the Girandoni Air Rifle or Girandoni air gun in literature (the name is also spelled "Girandony," "Giradoni"[2] or "Girardoni".[3]) 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. The air reservoir was a removable, club-shaped butt. The Windbüchse carried twenty-two .51 in (13 mm) lead balls in a tubular magazine. A skilled shooter could fire off one magazine in about thirty seconds, which was a fearsome rate of fire compared to a muzzle loader. A shot from this air gun could penetrate a one-inch wooden board at a hundred paces, an effect roughly equal to that of a modern 9 mm or .45 ACP caliber pistol.

Air gun power sources

Spring-piston air guns are able to achieve muzzle velocities near or greater than 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 effort.

Spring-piston guns operate by means of a coiled steel spring-loaded piston contained within a compression chamber, and separate from the barrel. Cocking the gun causes the piston assembly to compress the spring until a small hook on the rear of the piston engages the sear; pulling the trigger releases the sear and allows the spring to decompress, pushing the piston forward, thereby compressing the air in the chamber directly behind the pellet. Once the air pressure has risen enough to overcome any static friction and/or barrel restriction holding the pellet, the pellet moves forward, propelled by an expanding column of 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.

Spring-piston guns 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.[citation needed] 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 and drawing unwanted attention. Many shooters have found that velocities in the 800 - 900 ft/s (270 m/s) range offer an ideal balance between power and pellet stability.

Most spring piston guns are single-shot breech-loaders by nature, but multiple-shot guns have become more 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.

Spring guns, especially high-powered ones, have 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 recoil, since the recoil and "forward recoil" forces happen within milliseconds of each other, but it is infamous for the loosening or breaking of lenses and reticles found in low- and medium-priced telescopic sights. All mounted telescopic sights for air guns should be rated as such.

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

The better quality spring air guns can have very long service lives, being simple to maintain and repair. Because they deliver the same energy on each shot, their trajectory is consistent. Most Olympic air gun matches 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 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 lb/in² (14 to 21 MPa).

Multi-stroke

Multi-Stroke pneumatic air guns require 2-10 pumps of an on-board lever to store compressed air within the air gun. Variable power can be achieved through this process, as the user can adapt the power level for long, or short-range shooting. The design of higher quality and match-grade multi-stroke air rifles can propel a pellet to speeds in excess of 1,000 feet per second (300 m/s)[citation needed].

For beginners and intermediates, multi-stroke air rifles have been a cost-effective choice as they are generally the cheapest form of air gun available. Several manufacturers make multi-stroke air guns including, to name a few, Sheridan, Benjamin, Daisy, and Crosman. Modified multi-pump guns, with stronger pump linkages and improved valves, can produce muzzle energies in excess of 30 foot-pounds force.

Safety

For safety, CO2 containers must be kept at temperatures below 120 °F (49 °C) ; at temperatures above this level, the pressure begins to increase very rapidly, and can cause the container to fail. CO2 containers with diameters at or above two inches (50 mm) have a pressure release "rupture" mechanism to release the contents over a certain pressure level and avoid explosion because of high temperature. These disks are generally calibrated to a minimum pressure corresponding to the 120 °F (49 °C) level at 100% of the rated CO2 capacity. Elevated temperatures, even those below the critical temperature, can cause increased leaking through seals.