Air gun
There are three different power sources for modern air guns, depending on the design: spring-piston, pneumatic or bottled compressed gas (most commonly carbon dioxide and recently nitrogen).
A shot from this air gun could penetrate a one-inch-thick (2.5 cm) wooden board at a hundred paces, an effect roughly equal to that of a modern 9×19mm or .45 ACP caliber pistol.
[8][9] The increasing affordability of higher-power pre-charged pneumatic (PCP) rifles has allowed large projectiles and further target distance for competition purposes.
When shooting, the trigger is pulled and disengages the sear, allowing the main spring to decompress and release its stored elastic potential energy, pushing the piston forward, thereby compressing the air in the pump cylinder.
This often results in combustion smoke coming out of the muzzle and potential pressure damage to the rubber O-ring seals inside the gun.
Dieseling can be made to occur intentionally to increase power, by coating the pellet with lubricant or petroleum jelly, although this may result in damage to the breech seal.
Most spring-piston guns are single-shot breechloaders by nature, but multiple-shot repeaters with magazine feeders have been introduced in recent years by manufacturers such as Gamo, Umarex and Hatsan.
The spring itself is essentially a stand-alone enclosed piston pump without outlets and with pressurized air or inert gas (such as nitrogen) held tightly sealed within the cylinder.
When the gun is cocked, the gas inside the cylinder gets further compressed by the piston, stores potential energy and acts as a pneumatic accumulator.
During shooting, the hammer strikes the reservoir's release valve, allowing a set volume of the pressurized air to be discharged into the chamber and propel the projectile.
Having no significant movement of heavy mechanical parts during the discharge cycle, PCP airgun designs produce lower recoil, and can shoot as many as 100 shots per charge depending on the tank/reservoir size.
Early stand pump designs encountered problems of fatigue (both human and mechanical), temperature warping, and condensation – none of which are beneficial to accurate shooting or the airguns' longevity.
As a result, shot-to-shot consistency is maintained for longer than in an unregulated rifle, and the gun can also output more shots due to reduced waste of reservoir pressure.
Most CO2 guns use a disposable cylinder called a "Powerlet" cartridge, that is often purchased with 12 grams (0.42 oz) of pressurized CO2 gas, although some, usually more expensive models, use larger refillable CO2 reservoirs like those typically used with paintball markers.
This thermostability reduces the variation in output pressure associated with rapid successions of firing cycles, improving accuracy and reliability in extreme climates.
It also allows for higher shot consistency because each cartridge can be easily filled to an identical air charge, essentially removing the "power curve" of conventional PCP guns and bypassing any need for regulators.
[16] However, a small number of incidents relating to the alleged illegal conversion of (mainly) Brococks to allow them to discharge live ammunition sparked a media frenzy.
After the UK government implemented the Anti-Social Behaviour Act 2003 in January 2004, it became illegal to possess such airguns without a firearm certificate in the United Kingdom.
By far the most popular shape is the wasp-waisted diabolo pellet, which has two sections – a solid front portion called the "head", which contains the center of mass and is available in a variety of shapes and styles such as flat (wadcutter), round (domed), cone-shaped (pointed) and pitted (hollow point); and a hollowed, thin-walled conical rear portion called the "skirt", which expands and fully engages the bore to provide a good seal and thus allows maximal efficiency in pellet propulsion during shooting.
In flight, the skirt has greater drag-to-weight ratio than the head and exerts a rearward pull behind the center of mass, similar to that of a shuttlecock.
However, the diabolo shape also means that the overall pellet will have poor ballistic coefficient and tends to lose energy quickly and be more unstable especially in the transonic region (272–408 m/s ~ 893–1340 ft/s).
Diabolo pellets are conventionally made from lead, but are widely available in non-lead alternatives, such as tin, or a combination of materials such as steel or gold alloys with polymer tips.
Compared to the commonly used diabolo pellets, these slug pellets resemble cast bullets and have more contact surface with the bore and hence need greater propelling force to overcome friction, but have better aerodynamics, ballistic coefficient, and longer effective ranges due to the more aerodynamic shape, however they also require a fully rifled barrel for spin stabilization in flight.
Steel BBs can be acceptably accurate at short distances when fired from properly designed BB guns with smoothbore barrels.
Therefore, steel BBs lack the spin stabilization required for long-range accuracy, and usage in any but the cheapest rifled guns is discouraged.
Typically BBs are used for indoor practice, casual outdoor plinking, training children, or to save money, as they are significantly cheaper than pellets.
Replica CO2 pistols allow people to train with a BB gun, saving a lot of money to centerfire firearm cartridges.
Similar guns were also used briefly by the United States Army in a Vietnam-era instinctive shooting program called "Quick Kill".
Such air guns can shoot arrows at launch velocities rivalling or even exceeding high-end crossbows, while retaining consistency of precision unaffected by archer's paradox, but they are also more expensive to set up and maintain.
The modern pentathlon has since 2009 included a laser-run event that replaced the traditional cross country run of 3,200 metres and timed air-pistol shoot.
