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Basic Airgun Technology

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 180 fps to pneumatic guns firing 9 mm (and larger) lead bullets at well over 1200 fps, developing energy well into the .22LR range and beyond. The great majority of modern airguns are powered by springs and fire a .177 or .22 caliber pellet between 500 and 1000 feet per second, developing energies in the range of 5 to 20 foot pounds. That’s not much, considering that even the lowly .22 short develops around 80 foot pounds of energy, but it’s more than enough for a variety of target sports and even hunting small game.

Let’s start out with a discussion of the kinds of airgun powerplants that are used today.

Powerplants

The earliest air arms, dating back to at least the 17th century, used two basic systems which today we’d call ‘precharged 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 cylinder 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 recoilless 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. Vortek, of Farmington Hills, Michigan, briefly marketed a similar gas-strut system, some of which may still be found on the used market.

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 recoilless spring air gun. One system, pioneered by Feinwerkbau 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 system, pioneered by RWS/Diana, uses two pistons moving in opposite directions to cancel out recoil. However, careful balancing and tuning of spring size and transfer port size and shape, combined with spring dampening compounds and devices, can drastically reduce recoil in a standard spring gun.

Pneumatic Guns

In contrast to spring guns, pneumatic guns use a reservoir of compressed gas to propel a projectile. They are as a rule virtually recoilless, at least in any but the most powerful version, as the recoil energy of the projectile is dwarfed by the comparatively 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 reservoir. On firing, a hammer kicks a valve open and releases some or all of the air from the reservoir into the barrel. Pump pneumatics come in two basic varieties- single stroke, which require only one stroke of a lever to fill the reservoir, and multi-stroke models, which require multiple strokes to fill the reservoir.

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 quick to cock, efficient is their use of muscle energy, 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 reservoir 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 disposable CO2 cartridges, and those that are bulk-filled from a large tank. The guns using the disposable 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 disposable cartridge gun is basically a US type, for the most part. Disposable 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 notable 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 disposable cartridges, including such oddities as the Crosman CO2 shotgun.

One nice feature of CO2 is that it will maintain a constant gas pressure (about 900psi at room temperature) 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 suitable for indoor use only in colder weather. But in tropical climates it’s great- there are some very interesting CO2 guns made in the Philippines (see below)

A side note: There are two different types of CO2 cartridges that have been used for BB and pellet guns. The older guns used a small cartridge developed originally for making seltzer at home. Later guns used a larger cartridge developed specifically for air arms that contains gas and often a bit of lubricant as well. Crosman and Daisy and a few other makers sell these.

Bulk-filled CO2 guns

Bulk filled guns must be filled from an external reservoir 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 Philippines, a 28 gauge CO2 shotgun that can also fire saboted lead bullets or be fitted with a smaller caliber rifled barrel.

Precharged pneumatics

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 reservoir 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. In 1996 a small Swedish company started producing a three stage hand pump capable of charging pneumatic guns to 3000psi and beyond; this pump, distributed by RWS and others, has made owning a precharged pneumatic a much simpler affair, and I suspect these guns will become much more popular.

Unlike CO2 guns, compressed air guns are not self regulating, so a number of techniques are used to control shot-to-shot varience. The most straightforward way is to place a pressure regulator between the air resevoir and the chamber from which air will be released into the barrel. When the trigger is pulled, a spring loaded valve opens and dumps the contents of this chamber into the barrel. This is used in a relatively few guns.

The most common method is the simplest. On firing, a hammer strikes a spring-loaded air valve, opening it. The hammer bounces back to its resting position, and the chamber is then forced closed by the residual air in the resevoir. Properly tuned, this system is self regulating; as the pressure in the resevoir drops, the valve remains open for longer and longer periods.

Airsoft Guns

Airsoft guns use compressed gas or springs to fire a soft plastic ball specifially designed to be relatively harmless if it strikes a person or object. They were originally conceived as realist looking toys for countries such as Japan where there is strong interest in firearms, but any and all firearms ownership by ordinary citizens is strictly prohibited.

Modern Air Soft guns come in a dizzying variety of styles, and many are indistiguishable from the real firearms they seek to imitate. Such guns have found a place in realistic training, and in paintball-type competition. However, because of their low energies and limited accuracy they have no use in hunting or serious target shooting. Many people collect Airsoft guns as an alternative to collecting actual arms that are unavailable owing to cost or legal restrictions; airsoft guns are available that are almost indistinguishable from a wide variety of common military and fully automatic weapons.

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 (or “zimmerstutzen”) of the last century that fired a small caliber lead ball powered by a percussion cap alone. There were simple BB guns made around the middle of this century that used paper caps to propel the BB at low velocities, and I recall seeing a toy gun in the early 1960s that used paper caps to fire a cork ball.

The Mexican maker Industrias Cabanas produced 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 (though I believe the BATF calls it a firearm). At any rate, I have one, obtained by an FFL dealer for me from Mandall Shooting Supplies of Scottsdale, AZ, the sole importer, in the mid-1980s. Since acquiring mine I’ve periodically searched for another, but it appears that they are no longer made, at least by the maker of mine. I’ve managed to learn that Industrias Cabanas, S.A. in Aguilas, Mexico made them from 1949 to 1999, after which time the guns were no longer made.


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