Today there is a particular trend towards the use of pressurized air instead of CO2. Let me say from the start that I am still a strong believer in CO2. I can give you a lot of reasons why CO2 is still better but I can’t give many in favor of air. For example, A CO2 pistol or rifle is usually cheaper in original cost than an air model, it is simpler inside and has less to go wrong…..no gauges or regulators to worry about. There is little problem having CO2 supply tanks filled, any fire extinguisher shop will do it and it doesn't cost a lot. Some SCUBA shops will require you to be a member of a dive club or have insurance before they will fill an air tank for you. Before you buy, check out the cost of a CO2 cylinder vs. the cost of a SCUBA tank and DIN adapter, Also check out the cost of a 200 BAR. handpump, you will see that CO2 filling is much cheaper than air. CO2 pressures that you will be working with are around 800psi……air pressures are around 3000psi. There are precautions to take with both but the dangers using air are much higher. 

The argument in favor of air that the factories like to make is that the pressure of CO2 changes with temperature and air pressure does not. A lot of shooters have gotten a paranoia about it. If you look into this carefully you will find that it is technically correct but one would have to be shooting in under some very strange conditions before there would be a noticeable change of point of impact on the target due to temperature change in the cylinders. It can be shown, for example, that there is no noticeable change in the point of impact on the target over a temperature change of 15 degrees [from 55 to 70]. One is not likely to encounter this kind of change on a normal indoor range while he is shooting.

We have heard of shooters experiencing a noticeable change in point of impact for the first fifteen or twenty shots after changing cylinders or with the first shots on a warm rifle. [not so noticeable for pistol] It seems to be more pronounced on certain rifles. During the firing process CO2 tends to cool the pellet, chamber, bolt and other parts of the action. It is possible that there could be some velocity changes associated with this temperature change due to the length of time that it takes to "stabilize" the temperature of the mass. It would be more pronounced on a rifle due to the greater volume of gas used for each shot. Perhaps this is why CO2 was never accepted by the rifle shooters but was popular with the pistol shooter.

There is one advantage to air that should be considered, it is one that you never hear about and it may be the only good argument in favor of air, it has to do with barrel time. We are told that CO2 gas has a higher molecular coefficient of friction than does air. What this means is that when air is compressed and released it will spring back quickly because the molecules of air have little friction. When CO2 gas is compressed and released it springs back slowly because of the higher molecular friction. Another theory says that when air is released it simply has to expand…..when CO2 is released it has to “boil off” from liquid to become an expanding gas, the latter process is a slower one. If we translate this to an airgun situation it can be determined that the pellet acceleration in the barrel of an airgun will be faster than that in a CO2 gun…..even though the muzzle velocity is the same. The all-important barrel time in the airgun will be shorter and if the theory is correct, the airgun will be more “forgiving” than the CO2 gun. You may have noticed that when you fire a CO2 gun without a pellet the sound is sort of a “pop”, do the same with an airgun and there is definitely a sharper “crack”. This little-known feature of air is theoretically an advantage but it is probably a microscopically small one!!

Handpumps…… .They cost over 200 bucks and they will kill you!! Ever try to pump up a 200 BAR rifle cylinder?…….you could have a coronary!! The last thing in the world that you need before a match in an aerobic exercise!!! Another problem with handpumps is the possibility of moisture getting into the pistol. Pre-compressed air has not been in use long enough to tell yet but I predict that corrosion from moisture will eventually take place inside the aluminum cylinder presenting a major safety problem. I can forsee the necessity of inspecting the inside of the cylinders on a regular basis.

Obviously its my opinion that CO2 is still the best [at least for pistol]…..not convinced?….read the other two accompanying articles NOTES ON CO2 FILLING and NOTES ON AIR FILLING.