Shooting CO2 Match Pistols
Ten years ago CO2 was the preferred propellant for match air pistols at world class events. Gradually as the development of compressed air became more advanced, CO2 slowly fell from favor. These days it is considered outdated by many, and worse rumors are heard. But much of this attitude is simple ignorance on both its use and its proclaimed “inadequacies”. The inadequacies often quoted are really making mountains out of mole hills.
But the real advantage these days of CO2 is there are bargains to be found in “outdated” CO2 match pistols. For half the cost of most used CA guns you can buy a used CO2 model that 10 years ago was shooting scores at World Cup level that would still make Finals at today’s events.
There are actually some serious advantages to using CO2 over CA guns. Because cylinder pressures are roughly half that of a modern SCUBA filled guns, and because there is no need for a regulator on the pistol, service is required far less often. By the nature of the CO2 when compressed, it is a liquid. This makes weighing the cylinder a practical means of determining what is left of the charge in the cylinder. For as long as there is liquid left inside, the same pressure of gas is given off – thereby there is no slow tapering off of pressure leading to a gradual dropping of velocity as the cylinder runs low.
If the following rules are followed while filling CO2 cylinders, only extreme temperature conditions would conceivably cause any fluctuation in performance.
1. Chill the cylinder in the freezer for at least 10 minutes before filling. Ideally the cylinder should be 20 degrees Centigrade cooler than the ambient temperature around the bulk bottle. If this is done, there is no need to leave the cylinder attached with the valve open for any longer than a few seconds. Most bulk bottles have a siphon tube, since we're decanting a liquid here that will draw the liquid from the bottom of the bottle. Should the bottle not have a tube it will be necessary to turn it upside down while filling.
2. The cylinder must be weighed with a reasonably accurate set of scales. Empty and full weights will be stamped on the side of the cylinder. A set of electronic scales (most postal and kitchen scales are accurate enough) is all you need for this. Try to keep the weight to a few grams under the specified maximum weight. If you over fill the cylinder, there may be just liquid in the cylinder, allowing no room for gas to exist. In this case you must bleed the cylinder until the weight is back within tolerance – otherwise you may find the pistol can not meter any gas.
3. Do not let the pistol or cylinders get extremely hot or cold. In summer or winter it would be unwise to leave the gun box in the trunk of your car leading up to a match. The temperature extremes can cause expansion of the liquid, in effect overextending its capacity and giving similar problems to being over-filled. It can also affect the working pressure of the gun – but the general rule is, if you're okay in that temperature, your gun should be also.
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