Airgun

An airgun is a gun that accelerates its projectile by the rapid release of compressed gas.

History

Airguns have, in one form or another, been in use for thousands of years. The earliest design, which has been in use since prehistoric times, is the blowgun, consisting of a simple tube; the user blows through the tube to eject a poisoned dart at the target.

Designs for mechanical airguns began appearing in Europe in the early seventeenth century. These designs, like their predecessors, initially used darts as projectiles. By the eighteenth century, lead balls were standard ammunition for airguns.

In the spring of 1803, American Captain Meriwether Lewis purchased a Girandoni Windbusche in Philadelphia. This PCP-type .46 caliber airgun, manufactured in Austria for the military, could fire lead balls at 1000 fps (304 m/s). It was pressurized with 1,500 cycles of a hand pump. He brought the rifle on his 1803-1806 exploration, with William Clark, of the Louisiana Territory, demonstrating it for indigenous people whom the expedition encountered along the way.

The first mass-produced airgun was the "Challenger," constructed almost entirely of wood by the Markham Air Rifle Company of Plymouth, Michigan, in 1886. Two years later, the Plymouth Iron Windmill Company, located just steps away from Markham, was struggling to remain solvent; in order to boost windmill sales, they began manufacturing a metal airgun to give away with the purchase of a windmill. When the first model was tested by Plymouth Iron Windmill's general manager, Lewis Cass Hough, exclaimed, "Boy, that's a daisy!" (slang at that time for something extraordinary.) The company soon found that farmers were more interested in purchasing the airgun than an iron windmill, and the focus of the company shifted to manufacturing the Daisy Air Rifle. In 1895, the company changed its name to Daisy Manufacturing Company.

Types

Modern airguns fall into four basic categories, distinguished by their source of compressed gas: CO₂, variable pump, piston, and precharged pneumatic (PCP). Each type uses the same basic mechanism: with each discharge, a small amount of compressed gas is released to propel the projectile through the barrel.

CO₂ airguns draw their energy from a single-use cylinder of carbon dioxide. At 21°C(70°F) and 5.9 MPa(852.8 psi), carbon dioxide will be at the boundary between gas and liquid phases. The cylinder is pressurized to that level so that as gas is released in the operation of the airgun, the liquid carbon dioxide will vaporize and maintain nearly constant pressure. Because of this property, a single cartridge can be used for multiple shots. The Powerlet cartridge, designed by Crosman in 1950, contains 12 grams of pressurized CO₂, which can supply enough energy for 30 to 40 shots. CO₂ airguns are usually semiautomatic (one shot per trigger pull) but fully automatic (continuous fire while trigger is held down) and single-shot CO₂ guns are also common.

A variable pump airgun has a integral manually operated air compressor. Usually the handguard (the lower portion of the gun forward of the trigger) is used as a lever, which drives a piston to compress air in an onboard cylinder. The user can determine the relative power of the shot by the number of cycles of the pump, usually in a range from three to twelve pumps. Variable pump airguns are single-shot only; all of the energy from the pumping action is released in the shot.

Piston type airguns use spring action to rapidly compress the air behind the projectile. There are two primary types of piston: spring piston, which uses a steel coil, and gas piston, which uses a pressurized gas cylinder. Piston airguns have a barrel that is hinged at the breech; the barrel is linked to the piston, so that when the user "breaks" the barrel and folds the gun into a "V" shape, the piston is compressed and held in place by a latch. This action also allows access to the barrel breech, where the user loads the projectile. The barrel is then swung back into place, and when the trigger is pulled, the piston rod rapidly moves forward, creating pressure in the chamber, which pushes the projectile through the barrel.

A precharged pneumatic (PCP) airgun uses an external compressor to provide high-pressure gas to its onboard tank. For modern small-caliber airguns, PCP tanks are typically rated for 7-21 MPa (1000-3000 psi). This allows multiple shots without recharging; the number of shots depends on how much energy is released in each shot, and the pressure decreases with each shot. Although a larger tank or higher pressure would permit more shots between charging, the tank capacity and pressure rating is limited by weight, as most PCP airguns are intended to be carried by a single person.

Another common type of airgun is the paintball gun, which is not not addressed here.

Ammunition

Most general-manufacture airguns are of .177 caliber (4.5 mm); in common parlance, these tend to be called BB's. However, .22 caliber (5.56 mm) airguns are also common. Other calibers are available, up to .51 caliber (12.9 mm). Airguns larger than .25 caliber (6.4 mm) are considered "big bore."

Markham Air Rifle's "Challenger" and Plymouth's "Daisy" were initially made with .180 caliber barrels, in order to take advantage of existing lead birdshot of size BB. Later, as Daisy Airguns became more popular, the company prevailed upon shot manufacturers to make a smaller ball, .175 caliber, specifically for airguns, in order to reduce the cost of ammunition and the potential energy required for the gun. Daisy wanted the smaller caliber to be called "air rifle shot," but by that time consumers were accustomed to calling airgun ammunition "BB." In the 1920's, consumers began using steel ball bearings manufactured by American Ball Company; the ball bearings were lighter in weight and less expensive than lead shot. However, the ball bearings were not made to the same tolerances and would occasionally jam in the barrel. Daisy Manufacturing began making their barrels slightly larger, .177 caliber, to accommodate the steel ball bearings, and negotiated an agreement with American Ball Company to ensure stricter tolerances. Although it has never been a common caliber for firearms, .177 caliber remains the most popular size for airguns, the ammunition is still referred to as a "BB," and the airgun is commonly called a "BB gun."

In the late nineteenth century, some users began utilizing elongated ammunition with a piece of felt attached to the afterward end, similar to the dart. By the early twentieth century, ammunition manufacturers began offering lead pellets in the diabolo shape: a wide solid leading end, a narrow middle, and a hollow conical follower. This shape takes advantage of the aerodynamic properties of darts as well as the improved accuracy and range given by rifling. When a pellet is fired, the air pressure causes the conical follower to expand slightly and positively engage with the rifling of the barrel. Some airguns, such as the Crosman 2100, are designed to use either BBs or .177 caliber pellets.

Usage

Airguns are typically used for "plinking" (informal target practice). Users may set up paper targets or shoot at debris such as metal cans. In 1984, air rifle shooting was added to the Summer Olympics, with competitors shooting at a target 10 meters distant.

Military applications are limited to target practice. Because airguns have significantly less recoil than conventional firearms, as well as a much lower operating cost, some military forces use airguns for training.

Most airguns lack the power for hunting game. Small caliber airguns typically propel a projectile with 1-8 fpe (1.4-10.2 J)--barely enough to kill a small animal with an accurate shot. Small caliber airguns are commonly used for pest control, to kill rats, squirrels, small birds, etc. However, this should only be attempted by a skilled shooter using a highly accurate rifle, as an underpowered or inaccurate shot could merely wound the animal and leave it suffering in great agony rather than killing it humanely. However, high powered airguns can release enough energy to kill a large animal. The AirForce Texan .457 caliber boasts 600 fpe, which is more than enough to kill a large animal.

Because airguns do not use chemical combustion to propel a projectile, many governments do not categorize airguns as weapons; as such, they are subject to different regulations than firearms. For example, although in the United States private ownership of fully automatic firearms is heavily restricted, fully automatic airguns are readily available.

Hazards

All airguns are capable of causing serious injury or death. For example, in 1993, seven year old Joshua Moss was killed instantly when he stepped into the path of a BB fired by his cousin from a Crosman 760. The shooter stated that he had pumped the gun two or three times, which would yield kinetic energy of around 1 fpe (1.4 J), not usually considered lethal, but the path of the projectile carried it through the victim's eye socket and into his brain.

Airguns of .177 and .22 caliber typically make less noise than firearms, so in populated areas discharging an airgun is less likely to cause a nuisance. Furthermore, the discharge sound levels of most airguns do not warrant ear protection in adults. Some airguns include a noise suppressor which makes them even quieter. However, a projectile that exceeds the speed of sound (1125 fps or 343 m/s) will create a sonic boom which can be much louder than the initial discharge. The National Rifle Association recommends the use of hearing protection with all airguns.

Airguns are often manufactured to have the appearance of a firearm. On several occasions, police officers firing in self defense have shot a person carrying an airgun. In some areas, publicly brandishing an airgun that looks like a firearm is illegal.

Because of the hazards associated with airguns, users are advised to handle airguns as they would firearms, applying the same safety protocols.

In Popular Culture

The 1983 movie A Christmas Story features the protagonist, nine year old Ralphie Parker, who hopes to receive a Daisy Red Ryder BB gun for Christmas. He is admonished by several adults that "You'll shoot your eye out!" but nevertheless is given the airgun for Christmas and promptly breaks his eyeglasses with a ricochet.