What Is An Airgun
Although modern airguns differ markedly from early versions, the basic principles utilized in the construction of airguns have been employed for centuries. The essential feature is that compressed air is stored in the gun until the time of firing. At that time, the gas is released behind the projectile which propels it down the barrel. The major difference between types of air rifles is how the air is compressed and where it is stored. Some of the early air rifles had a reservoir (in some cases, the rear section of the stock and in others a hollow sphere located below the action) in which air compressed by use of an external pump was stored. Part of the air could be discharged behind a projectile to drive it forward. Some of the early air rifles utilized projectiles of .30, .35, or even larger caliber. Air rifles of this type were used in Europe in the late 1500s, and Lewis and Clark took such an air rifle on their historic Voyage of Discovery in 1804-1806.
Production of American BB guns began in the late 1800s. Most of these low-powered models are cocked by some sort of lever which pulls back a piston against a spring. The piston in some cases is little more than a washer with a leather collar that makes the piston have an almost air tight seal inside the barrel. At the time of firing, the piston is pushed forward by the spring to compress air behind the BB which projects it out of the barrel. Most such guns are low in power and they are used for recreational shooting and pop can punching.
From a technical point of view, any gun that launches projectiles utilizing compressed gas rather than producing gases burning a propellant (powder) is considered to be an “air” gun. In some cases, the propelling gas may be carbon dioxide in which case the gun is actually a “gas” gun, but the term airgun is still generally applied to them. One of the great American airgun designs is the multi-pump (sometimes called a “pump up” gun) in which air is compressed by a series of pump strokes. When the gun is fired, the compressed air enters the breech behind the projectile driving it forward. This type of rifle has been produced for well over a century, and with a maximum number of pump strokes, some of these rifles are powerful enough to be useful tools in hunting.
Another popular type of powerful air rifle is the break action (also known as the spring piston or break barrel). With this type of air rifle, the barrel functions as a lever that is pulled downward to force a piston inside the receiver backward by means of a linkage. This moves the piston to the rear as it compresses a strong spring or, as in the case of the Nitro Piston®, a gas. At the moment of firing, the piston that compresses the air is driven forward by the spring which compresses air behind the pellet driving it down the barrel. Other variants of this design utilize a lever along the side of the rifle or under the barrel as the cocking lever.
About half a century ago, Crosman Corporation pioneered the use of a small cylinder that contained compressed carbon dioxide (CO2) as the power source in pellet rifles. Known as the Crosman Powerlet®, each cylinder holds 12 grams of CO2 and that amount is sufficient to fire a considerable number of shots simply by cocking the rifle and loading a pellet. This characteristic is shared with the PCP rifles in which a reservoir holds enough compressed air for firing several shots.
Jim House began shooting with a single shot BB gun at a very early age. Now, seventy years later, he is an airgun enthusiast. After a 32-year career as a chemistry professor at Illinois State University, he has written extensively about shooting sports, which has resulted in the books American Air Rifles and CO2 Pistols and Rifles. His books also include The Gun Digest Book of 22 Rimfire and, with his wife Kathleen, Customize the Ruger 10/22. Jim is the Reloading Editor for Gun World magazine and a Contributing Editor for The Varmint Hunter Magazine, The Backwoodsman, Airgun Hobbyist, and The Illinois Shooter. Although a lot of his work is with firearms, he maintains a keen interest in airgunning while also serving as Adjunct Professor of Chemistry at Illinois Wesleyan University.