Most shooters are familiar with some sort of air gun- usually the Daisy BB gun they had (or coveted) as a youth. The luckier ones had access to a higher-powered pellet gun, perhaps a pump-up gun from Sheridan or Benjamin, or a CO2 gun from Crosman.
Today there's a tremendous variety of air guns available, ranging from $10 spring guns that shoot BBs or pellets at 180fps to pneumatic guns firing 9mm lead bullets at well over 1200 fps, developing energy well into the .22LR range. This FAQ is designed to give the reader an overview of the technology and the range of modern air arms.
Powerplants
The earliest air arms, dating back to at least the 17th century, used two basic systems which today we'd call 'prechared pneumatics' and 'spring air' guns. Today there's a much wider variety, but most if not all bear a strong resemblance to those original types.
Spring-Air guns
Spring-air guns develop power via a piston propelled by a spring under compression. Cocking the weapon causes a piston to be drawn back in a cylinder, drawing air into the cyliner and compressing a coil spring. Pulling the trigger releases the piston, allowing the spring to propel it forward and force a large volume of air through a hole into the barrel, propelling the pellet down the barrel.
Spring air guns can be as simple as a BB gun or as complex as a recoiless match air rifle. They can be simple, low powered guns or high-power rifles developing 30+ ft/lb of energy. In one modern design (Theoben) the coil spring is replaced by a gas strut containing air or nitrogen under pressure.
Spring air guns generally develop a significant of recoil from the action of the movement of the piston, but it is possible to produce a recoiless spring air gun. One system, pioneered by Feinwerbau in their 300B series of match rifles allows the entire action to slide on a set of rails. When the gun is fired, the barrel and action are allowed to slide rearward under recoil, while the stock remains motionless. This system is also used to RWS and Air Arms in some of their rifles. The other sysyet, pioneered by RWS/Diana, uses two pistons moving in opposite directions to cancel out recoil.
Pneumatic Guns
In contrast to spring guns, pneumatic guns use a resevoir of compressed gas to propel a projectile. They are as a rule virtually recoiless, at least in any but the most powerful version, as the recoil energy of the projectile is dwarfed by the comparitively huge mass of the gun. As a consequence, pneumatic guns are the choice for most types of target shooting.
Pneumatics are also generally much nosier than spring-air guns, as a much larger volume of gas is released along with the pellet. This noise can be reduced via external or built in silencers.
Pump Pneumatics
In pump pneumatic guns the shooter works a lever or piston to compress air into a resevoir. On firing, a hammer kicks a valve open and releases some or all of the air from the resevoir into the barrel. Pump pneumatics come in to basic varieties- single stroke, which require only one stroke of a lever to fill the resevoir, and multi-stroke models, which require multiple strokes to fill the resevoir.
Single stroke pneumatics range from a few inexpensive Daisy and Crosman guns up through expensive field guns like the Dragon and match guns like the RWS 100. Single stroke guns have the advantage of being quicker to cock and having a high degree of consistency from shot to shot.
Multi-stroke pneumatics are generally found more at the lower end of the scale, ranging from around $30-$100 in price, though there are exceptions. Most are inexpensive guns from Daisy and Crosman, though there are the mid-priced guns from Sheriden and Beeman, slightly higher priced guns like the Sharp models from Japan, and unusual guns like the Korean Yeehwha shotgun. Multi stroke pneumatics offer higher power than single stroke guns, and the option of variable power as a varying number of strokes can be used to charge the gun. This is not necessarily an advantage, as trajectory changes radically with power level.
Gas Guns
Another class of guns derives energy to propel a projectile from a resevoir that has been filled with a compressed gas from some external source- usually CO2 or simply compressed air, though other gasses can, and have been used. Generally the guns are designed to use either CO2 or air, although it is possible for some guns designed for one source to use another.
CO2 guns
CO2 guns come in two varieties- those that use the small disposeable CO2 cartriges, and those that are bulk-filled from a large tank. The guns using the disposeable cartridges are again to be found mainly at the low of the price range, and include a number of inexpensive models from Daisy, Crosman and Marksman in the US, and a few other makers elsewhere in the world. The disposeable cartridge gun is basically a US type, for the most part. Disposeable cartridge guns today are found mostly at the low end, though there are some interesting guns to be had in the middle price range, most noteable the new Crosman 10/77, a CO2 clone of the popular Ruger 10/22 rifle. In past years there was a wider variety of higher-power guns using disposeable cartridges, including such oddities as the Crosman CO2 shotgun.
One nice feature of CO2 is that it will maintain a constant gas pressure as it transitions from a liquid to a gas. This makes complex pressure regulation unnecessary. The downside is that CO2 has a near-zero vapor pressure at cold temperatures, making guns that use CO2 suitible for indoor use only in colder weather.
A side note: There are two different types of CO2 cartridges that have been used for BB and pellet guns. The original guns used a smaller type of cartridge developed ogiginally for making seltzer at home. Later guns used a larger cartridge developed specifically for air arms, gewnerally called a 'powerlet', that contains gas and often a bit of lubricant as well.
Bulk-filled CO2 guns
Bulk filled guns must be filled from an external resevoir of CO2. MOst bulk filled guns are match pistols and rifles, though there are also some very unusual guns designed for hunting using CO2, mainly from countries with laws that make it difficult to own firearms. One of the best known is the Farco shotgun from the Phillipines.
Precharged pneumtics
While the term 'precharged pneumatic' could, technically speaking, refer to a wide variety of gun types, the term generally refers to a gun which is filled from an external tank of compressed air- usually a SCUBA tank. Precharged guns are basically a British invention, and while guns using a resevoir of compressed air have been around for a couple of centuries, most modern precharged pneumatics seem to derive from a modified gun that was designed for shooting tranquilizer darts through a large smooth bore. The top levels of field target shooting today are dominated by precharged pneumatics, though classes exist for other types of guns as well.
Oddballs
There are always some types of guns that defy classification, as gunsmiths are such an inventive lot. One such gun derives from the low-powered parlor rifles of the last century that used a small caliber lead ball powered by a percussion cap alone.
The Mexican maker Cabanas produces a range of guns that fire a .177 caliber lead ball propelled by a .22 blank cartridge. This is really neither a modern cartridge gun, a muzzleloader nor an air rifle, but it can fire the heavier types of pellets, so I suppose it is a pellet gun. At any rate, I have one, and it's loads of fun.
mje@pass.wayne.edu
mje 6/21/95