There are three basic types of airguns; pneumatic pump guns, precharged pneumatics and spring piston.
Pneumatic pump guns
Pneumatic pump guns store compressed air in a reservoir which is emptied for each shot. Depending on the gun design, it may require 1 or more pumps to fill the reservoir.
With multi pump air guns, it is possible to regulate the velocity somewhat based on the number of pumps but pumping can become rather tedious with a long string of shots. Multipump pneumatic guns are often your least expensive option for an air rifle with some models retailing for less than fifty dollars.
PCP or precharged pneumatic air guns use a regulated volume of gas dispensed from a pressurized container of air or carbon dioxide. Most air pistols and some rifles of this type will use small disposable cylinders containing 12 grams of carbon dioxide. Some of the more expensive guns will have a permanent gas container affixed to the gun which can be recharged using a compressor or tank.. For those guns, which use the 12 gram cylinders, it has been my experience that once a cylinder is punctured, the gas will leak out within a few days.
The spring piston is the simplest type of airgun mechanism made. Most cheap BB guns as well as some more expensive target air rifles and pistols use this method of propulsion.
In essence, a spring is compressed, when it is released by the trigger mechanism, the spring quickly pushes a piston into a cylinder with a narrow apeture at the other end. This squirts a puff of air against the base of the projectile, causing it to travel down the barrel. The primary controlling factor of the velocity developed will be the strength of the compressed spring.
While inexpensive to manufacture and relatively maintenance free, they are not for everyone. Spring piston pneumatics require a period of use in order to achieve the most accuracy possible and they can be very hard on scopes.
Many spring piston air rifles sold today are unnecessarily powerful for target shooting at the standard competition distance of 10 meters. Also they require a significant cocking effort, sometimes in excess of 40 pounds. This can be fatiguing over a series of shots.
More on Spring Piston Air Rifles
Air Gun Calibers and Projectiles
Air guns have been produced in an variety of designs and calibers since at least the 18th Century. Today however 0.177, 0.20, 0.22 and 0.25 are the only calibers in widespread use with 0.177 caliber by far the most common and popular choice.
By far the most common pellet type used today is the Diablo or wasp waisted projectile. Generally made of soft lead or lead alloy, the diablo air gun pellet is a rather unique projectile. It has a hollow skirt, designed to be flared by the propelling charge of air or gas so that it will engage the rifling of the bore while producing the least amount of friction. If you are able recover an undeformed pellet fired into the water or some other soft media, you will see that there are only very slight rifling marks on the skirt and nose of the projectile.
Lead BB's shot size corresponding to 0.180 inch diameter lead ball. Steel BBs measure 0.173 inch, do not engage the rifling.
|0.177 Caliber Pellet|
|Metric Designation||4.5 mm|
|Typical Pellet Diameter (inches)||0.177|
|Typical Pellet Weight (grains)||7.9 grains|
|Pellet Weight Range (grains)||5.1 - 12.0|
|0.200 Caliber Pellet|
|Metric Designation||5.0 mm|
|Typical Pellet Diameter (inches)||.200|
|Typical Pellet Weight (grains)||11.4|
|Pellet Weight Range (grains)||9.2 - 15.6|
|22 Caliber Pellet|
|Metric Designation||5.5 mm|
|Typical Pellet Diameter (inches)||.218|
|Typical Pellet Weight (grains)||14.3|
|Pellet Weight Range (grains)||12.6 - 29.1|
|0.250 Caliber Pellet|
|Metric Designation||6.25 mm|
|Typical Pellet Diameter (inches)||.250|
|Typical Pellet Weight (grains)||21.6|
|Pellet Weight Range (grains)||17.7 - 37.0|
Competitive Air Gun Shooting
Formal airgun (rifle and pistol) competitions are generally conducted as a distance of 10 meters (33 feet). While that might not seem to be very far, a great deal of precision is required by the shooter in order to be competitive. Consider that a standard NRA approved 10 Meter air pistol target has a scoring ring diameter of about 6 inches and a ten ring only 2/10ths of an inch or 5 milimeters in diameter.
The width of a Standard Air rifle lane is generally 48 inches or wider. While the permissible minimum is 40 inches, lanes this narrow make firing prone difficult.