Editing Accurizing (section)

==Airgun powerplants==
The difference between an airgun and a firearm is the way in which the power to launch the projectile is provided. In a firearm the projectile propulsion is provided by an exothermic chemical reaction, and in an airgun is it provided primarily by mechanically compressed gas, typically either air or [[carbon dioxide]] (CO<sub>2</sub>), though these gases are used primarily for convenience and some airgun variants run on other gases, such as [[refrigerant]]s like [[1,1,1,2-Tetrafluoroethane|R-134a]] commonly used in [[airsoft]] guns, or [[hydrogen]] used in [[light-gas gun]]s.

There are three primary types of powerplant used in airguns:
*Spring-piston, which uses a spring-loaded piston to compress air within an [[air pump]] at the moment of firing
*Pneumatic, which uses pre-compressed air stored in a reservoir within the gun
*Compressed gas, which uses a small removable [[gas cylinder]] now ubiquitously stores liquid [[carbon dioxide|CO<sub>2</sub>]] ([[Powerlet]])

Each method has its own advantages and disadvantages, and different areas that can be addressed to ensure consistency.<ref name=airguntypes>{{cite web |url=http://www.airguns.net/general_airgun_types.php |title=The Three Basic Types of Airguns |author =Ben Saltzman |publisher=American Airguns |accessdate=2007-09-13| archiveurl= https://web.archive.org/web/20071015143244/http://airguns.net/general_airgun_types.php| archivedate= 15 October 2007 | url-status= live}}</ref>

The most powerful systems will produce velocities near or exceeding the [[speed of sound]] with lightweight pellets; this, however, is not a good thing where accuracy is concerned. The commonly used airgun diabolo pellets have a poor [[ballistic coefficient]], and quickly lose velocity; when they drop below the speed of sound, they will often tumble. However, high velocities sell airguns; if accuracy is desired from these high velocity guns, then heavier pellets should be used to keep the velocity down. This will provide not only better accuracy, but better downrange preservation of velocity and kinetic energy.<ref name=airguninnacuracy>{{cite web |url=http://www.airguns.net/general_inaccuracy.php |title=Inaccuracy in Airguns |author =Lewis Reinhold |accessdate=2007-09-13| archiveurl= https://web.archive.org/web/20071020202640/http://airguns.net/general_inaccuracy.php| archivedate= 20 October 2007 | url-status= live}}</ref>

===Pneumatic===
Pneumatic systems use compressed gas for power, usually compressed air. This air may be compressed by the gun for each shot, in a ''single stroke'' or ''pump'' (multiple stroke) gun, or it may be ''precharged'' by an external compressor.

A single stroke system, as the name implies, uses a single stroke of the pump to compress a cylinder full of air, which is then all used for one shot of the gun. Single stroke systems are both inexpensive and capable of high accuracy due to the simplicity and consistency of the single stroke design.<ref name=airguntypes /> The downsides are the low power provided, though this is not a handicap in standard 10 meter airgun target shooting. When [[Daisy Outdoor Products|Daisy]] introduced an inexpensive single stroke pistol, the model 717, in the late 1970s, American [[Olympic Games|Olympic]] shooter Don Nygord demonstrated the potential of the design by shooting an accurized version in a California State air pistol championship, and winning the gold medal. The (at the time) US$40 Daisy, with a better rear sight and an adjustable trigger added, shot as well as the US$400 Olympic class air pistols it was competing against.<ref>{{cite journal |title=How to Make a Super Shooter: How to Accurize Your Daisy 717 For Practically Nothing and Outshoot the High Priced Competition |last=Nygord |first=Don |date=April 1980 |journal=American Marksman}}</ref>

More powerful is the pump system, which is a slightly more complex version of the single stroke design. Rather than leaving the air in the piston when compressed, the pump airgun has a reservoir to contain the compressed air, allowing multiple pumps to be used, typically 2 at a minimum, up to 10 pumps for full power. The ability to vary the power, however, is the pump airgun's major disadvantage when it comes to accuracy, as it makes it very difficult to get a consistent charge.<ref name=airguntypes /> The increased power of a pump airgun makes it an attractive choice for many shooters, and there are steps that can be taken to improve consistency, such as modifying the air chamber so that not all the air is exhausted in a shot.<ref name=steroid>{{cite web|url=http://www.mac1airgun.com/steriodags.html |title="Steroid Modified" BENJAMIN/SHERIDAN |accessdate=2007-09-13 |archiveurl=https://web.archive.org/web/20070827001149/http://www.mac1airgun.com/steriodags.html |archivedate=27 August 2007 |url-status=dead }}</ref>

The last type of pneumatic airgun is the precharged pneumatic. This is both an old and a new design; some of the earliest airguns, such as the model carried by [[Lewis and Clark]], were of this type, as are many new cutting edge models. The precharged pneumatic uses an external source of compressed air, either an external pump or a high pressure reservoir such as a [[Diving cylinder|SCUBA tank]], to fill a reservoir. The reservoir can be a small, single-shot one, such as in the Brocock Air Cartridge system, or a large, multi-shot tank. The key to top accuracy in a precharged pneumatic is a consistent pressure. With multishot systems (as are most), the pressure in the reservoir will drop with each shot fired, so the best way to achieve consistency is with a [[pressure regulator]], which provides a steady, but lower, pressure at the valve, for as long as the reservoir pressure remains higher than the regulated pressure. Regulators are also generally adjustable, so a low pressure setting will provide many shots of lower power, while a high pressure setting will provide a few high power shots.<ref name=airguntypes /><ref name=pcpregulator>{{cite web |url=http://www.airguns.net/general_regulators.php |title=Airgun Regulator Basics |accessdate=2007-09-13| archiveurl= https://web.archive.org/web/20071020202651/http://airguns.net/general_regulators.php| archivedate= 20 October 2007 | url-status= live}}</ref>

===Piston===
Piston airguns, often called "springers", are unique in many ways. Since the firing process involves a fairly massive piston suddenly moving to compress the air, they have a significant "kick", generally called "recoil" (though this is not the same as firearm recoil). The recoil begins when the piston starts to move forwards, which pushes the rest of the gun backwards. The recoil then stops suddenly as the piston reaches the end of its travel, and is brought to a stop by the cushion of high-pressure air trapped between the piston and pellet. This recoil can be brutal on the gun in high-powered models, and will loosen screws, shift sights, and break scopes not designed specifically for the unique recoil of piston airgun&mdash;all of these can lead to poor accuracy. In addition to the recoil, piston airguns have a long lock time, as the piston must compress the air before the pellet begins to move, and the gun is moving due to the recoil during this time. Spring airguns require a special technique to fire, to ensure that the gun moves very consistently during this recoil. The preferred method is a very loose hold, to allow the gun to move back; this means that a piston airgun will ''not'' shoot the same from a bench. All accuracy testing and sighting in must be done in the same position the gun will be shot from, otherwise the results will be different.<ref name=airguntypes /> 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.<ref name=rws54>{{cite web |url=http://www.pyramydair.com/cgi-bin/model.pl?model_id=398 |title=Diana RWS-45 |accessdate=2007-09-13| archiveurl= https://web.archive.org/web/20071011072824/http://pyramydair.com/cgi-bin/model.pl?model_id=398| archivedate= 11 October 2007 | url-status= live}} The RSW-54 is a model 48/52 with the action mounted on rails, so it can recoil within the stock.</ref>

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.<ref name=gasspring>{{cite web |url=http://www.pyramydair.com/blog/2006/04/gas-springs-of-theoben-airguns.html |title=Gas springs of the Theoben airguns! |date=13 April 2006 |accessdate=2007-09-13| archiveurl= https://web.archive.org/web/20070812174325/http://www.pyramydair.com/blog/2006/04/gas-springs-of-theoben-airguns.html| archivedate= 12 August 2007 | url-status= live}}</ref> 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<ref name=r1tune>{{cite web |url=http://www.pyramydair.com/blog/2006/08/spring-gun-tune-part-13-range-testing.html |title= Spring gun tune: Part 13 Range-testing the R1 we tuned |date= 15 August 2006 |accessdate=2007-09-13| archiveurl= https://web.archive.org/web/20071013174956/http://pyramydair.com/blog/2006/08/spring-gun-tune-part-13-range-testing.html| archivedate= 13 October 2007 | url-status= live}} Contains links to all sections of article on the tuning of an R1 air rifle</ref>

===CO<sub>2</sub>===
CO<sub>2</sub> 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. CO<sub>2</sub>'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 CO<sub>2</sub> 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.<ref name=airguntypes />

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 CO<sub>2</sub> airguns were filled from an external source of CO<sub>2</sub>, but in 1954 [[Crosman]] introduced the 12&nbsp;gram [[Powerlet]], a compact, disposable tank now ubiquitous in inexpensive CO<sub>2</sub> airguns. The downside to these is that the small quantity of CO<sub>2</sub> liquid cools down quickly, leading to a rapid drop in velocity and a changing point of impact. By moving to a bulk fill system, with a much larger tank, there is more liquid available, and the greater mass will cool far more slowly.<ref name=mac1ld>{{cite web|url=http://www.mac1airgun.com/ldpistol.html |title=The Mac1 LD Air Pistol |accessdate=2007-09-13 |archiveurl=https://web.archive.org/web/20070826205903/http://www.mac1airgun.com/ldpistol.html |archivedate=26 August 2007 |url-status=dead }}</ref>
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