be done in the same position the gun will be shot from, otherwise the results will be different. Piston airgun recoil cannot readily be dealt with without a significant redesign; in some cases the action can be mounted on a sliding rail, or two counter-recoiling pistons can be used, but this requires significant changes to the design. The resulting gun will be far less sensitive to the shooter's hold, and thus much easier to shoot accurately. The first step to accuracy of a piston gun is to ensure that all screws are secure and the sights are rated for use on a piston airgun. Another potential issue regarding accuracy is resonance in the spring used to power the piston in most airguns. The spring will vibrate strongly as the piston stops, and this will affect the harmonics of the gun. A gas spring will, if one can be fitted to a given model, provide vibrationless action, though with some loss of efficiency and even sharper recoil. Spring driven pistons also respond well to accurizing; careful fitting of parts and use of quality lubricants and spring damping tar can reduce the level of vibrations and improve accuracy CO2 CO2 is commonly found in multishot airguns, from the cheapest plinkers to Olympic class target guns, though the latter are facing competition from regulated precharged pneumatics. CO2's advantage is that it is stored in a liquid form, rather than a gas, and as such provides a greater power density. The liquid also provides a constant pressure, the vapor pressure, as long as there is liquid remaining in the reservoir. The downside to CO2 is that it is dependent upon the vapor pressure, which changes significantly with temperature. This is of primary concern to outdoor shooters, who may shoot in widely varying temperatures, or for rapid fire shooters, as rapid release of the gas results in a rapid drop in the temperature of the liquid. The issue of temperature change is not readily addressable, other than by the use of readily adjustable sights, so the shooter can adjust the sights to match the point of impact based on the current ambient conditions. In the case of rapid fire, there is a solution that can provide far greater stability for many guns. The original CO2 airguns were filled from an external source of CO2, but in 1954 Crosman introduced the 12 gram Powerlet, a compact,