AIRGUNOMICS 411

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THE RESOURCE CHANNEL FOR AIRGUNS, ACCESSORIES & REVIEWS

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Pre-charged pneumatic[edit]

Pre-charged pneumatic air guns (PCPs) have their internal reservoir pre-filled from an external air source (such as a diving cylinder or air compressor, or by manual charging with a high-pressure stand pump), and remain pressurized until depleted after repeated shooting. During shooting, the hammer strikes the reservior's release valve, allowing a set volume of the pressurized air to be discharged into the chamber and propel the projectile. Depending on the release valve design, PCP air guns can be categorized into two types – unregulated and regulated (which has either a mechanical or electronic regulator valve). In addition to compressed air, custom PCP models using compressed pure nitrogen and even compressed helium have also been recently developed.

Because of the need for cylinders or charging systems, PCP guns have higher initial costs but much lower operating costs when compared to CO2 rifles, and have superior performance over ordinary pump guns. 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. The ready supply of air has allowed the development of semi- and fully automatic air guns.[9] PCP guns are very popular in Europe because of their accuracy and ease of use. They are widely utilized in ISSF 10 metre air pistol and rifle shooting events and the sport of Field Target shooting,[10] and are usually fitted with telescopic sights.

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. Modern stand pumps have multi-stage chambers and built-in air filtration systems and have overcome many of these problems. Using scuba-quality air decanted from a diving cylinder provides consistently clean, dry, high-pressure air.

During the typical PCP's discharge cycle, the hammer of the rifle is released by the sear to strike the bash valve. The hammer may move rearwards or forwards, unlike firearms where the hammer almost always moves forward. The valve is held closed by a spring and the pressure of the air in the reservoir. The pressure of the spring is constant, and the pressure of the air released (which is also known as the working pressure) decreases with each successive shot. As a result, when the reservoir pressure is high, the valve opens less fully and closes faster than when the reservoir pressure is lower, resulting in a similar total volume of air flowing past the valve with each shot. This results in a degree of partial self-regulation that gives a greater consistency of velocity from shot to shot, which corresponds to the middle "plateau" phase of the gun's shot-to-shot muzzle velocity profile (also known as the power curve ). Well-designed PCP will display good shot-to-shot consistency over a long period, as the air reservoir is being depleted.

Other PCP rifles and pistols are regulated, i.e. the firing valve operates within a secondary chamber separated from the main air reservoir by the regulator body. The regulator maintains the pressure within this secondary chamber at a set pressure (lower than the main reservoir's) until the main reservoir's pressure drops to the point where it can no longer do so. 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.[11]