Air gun

Air guns are weapons that propel a bullet using compressed air or an other, possibly liquefied, gas. They are also called pneumatic guns, pellet guns, or BB guns.

There are many different types of air guns: spring-piston, multi-pump pneumatic, precharged pneumatic (PCP), and reservoir.

Pneumatic rifles have been around since the 15th century. It has been well documented that Austrian soldiers sniped and killed French soldiers under Napoleon Bonaparte with them.

Table of contents

1 Spring piston guns
2 Cylinder guns
3 Reservoir guns

Spring piston guns

Spring-piston air guns achieve muzzle velocities near the speed of sound from a single, not-too-difficult cock.

Cocking a spring-piston gun compresses a large steel spring inside the gun. The trigger releases the spring. The spring moves a piston, which instantaneously compresses the air in a chamber. The hot (often exceeding 1000°C) air moves the pellet down the bore of the gun. There are no adiabatic losses because the air does not have time to cool. This high efficiency is why the gun is so easy to "pump." The piston and cylinder of a spring-piston air gun must be lubricated with a special oil that will not burn at these high temperatures. Spring-piston guns seem to have a practical upper limit of 1200 ft/s (370 m/s) for .177 cal (4.5 mm) pellets.

Most spring piston guns are single shot breech loaders by nature (somewhat like an old shotgun) but multiple-shot weapons have been increasingly common in recent years. Spring guns are typically cocked by a mechanism is which the gun is hinged at the mid-point, with the barrel serving as a cocking lever. Other systems used include side levers, under-barrel levers and motorized cocking, powered by a rechargeable battery.

The better quality spring air guns can have long service lives, often exceeding thirty years. Because they deliver the same energy on each shot, the trajectory is extremely repeatable. This repeatability resulted in most Olympic air gun matches through the 1970s and into the 1980s being short with spring-piston guns. Beginning in the 1980s, guns powered by compressed, liquified carbon dioxide began to dominate competition. Today, the guns used at the highest levels of competition are powered by compressed air stored at very high pressures of 2000 to 3000 lb/in² (14 to 21 MPa).

The Chinese army uses spring piston small arms to train more economically. Surplus military-issue chinese spring-piston air-guns are sometimes widely available by mail-order.

Since some spring-piston guns have muzzle velocities near the speed of sound, the normal bullet is a "pellet" shaped like two cones joined at the apex. This shape is optimally stable near the speed of sound- it does not tumble.

Most spring piston air guns have a calibre of .177 (4.5 mm), and are designed for target practice. Cost per round is less than $0.02 (US) for olympic-quality ammuntition, and far less for cheaper grades. .20 .22 and .25 calibre (~5.1, ~5.6 and ~6.4 mm) guns exist, and are used mainly for hunting and fieldtarget shooting.

Cylinder guns

Cylinder guns shoot from a purchased cylinder, usually filled with liquefied carbon dioxide. Most paintball guns are this type. There are also CO₂ charged airguns that are very popular for plinking. PCP (pre-charged pneumatic) airguns can be used for hunting and competition. These are usually filled from an air reservoir, such as a diving cylinder.

A gas gun has also been used in space on EVAs for moving around, e.g. the Hand-Held Maneuvering Unit (HHMU), using compressed oxygen, and the Crew Propulsive Device (CPD), using compressed nitrogen.

Reservoir guns

Reservoir guns, sometimes called "multi-pump" guns, have a pump to compress air into a reservoir. The air cools, losing much of the energy. These are neither fun nor fast. If a single shot needs more than one pump, it's probably a reservoir gun.

Most reservoir guns use the same ammunition as spring-piston guns.

Most historical air-guns were reservoir guns. The air gun carried by Lewis and Clark was a reservoir gun.

Many reservoir guns have been used for hunting. One of the traditional weapons for hunting wolves in Russia was said to be a large-calibre reservoir air-rifle. It is said to have shot silently to avoid warning the pack. Modern resevoir guns in larger calibers (6 mm to 9 mm) are often used for hunting small game.

In the days of Louis XIV of France, reservoir guns were truly fearsome, as they could be fired in all weather (unlike flintlocks), and could shoot through armor. In this era, France had a special detachment of snipers who carried air-rifles.

The multi-pump and CO₂ pneumatics have been popular in the United States, where they are known as "BB guns" or "pellet guns," depending upon the type of projectile used. These are typically viewed in other countries as children's toys. There are exceptions to this, as companies such as Benjamin Sheridan, Crosman, and Daisy market sophisticated systems (though Daisy and Crosman, also manufacture children's guns). Most airguns can be practiced in a backyard or garden, and even indoors with the proper backstop. Some of the stronger power "springers" can propel a pellet beyond 1100 ft/s (340 m/s) at approximately the speed of sound. It will produce a noise similar to a .22 cal (~5.6 mm) rimfire. These pneumatic rifles can be found in the following calibers, .177 (~4.5 mm) most common, .20 (~5.1 mm) Benjamin sheridan, .22 (~5.6 mm) most common for hunting, .25 (~6.4 mm) and even 9 mm.