Winning the Cold War
The battle between CO2 and the thermometer Part 1 Part 2
By Dennis Adler
I have two things in common with CO2; I don’t function well in cold weather or extreme heat. CO2 likes to be at an optimum temperature range of no less than 60 degrees and no greater than 90 degrees. That’s actually the extreme ends, between 70 and 80 degrees is really where CO2 functions best. When the temperature gets above 80 degrees, pressure (PSI) increases with CO2; the upshot is you also get slightly elevated velocities and at around 90 degrees you begin to see vaporization of the CO2 leaving the barrel (very cold air meeting very hot air). This looks like a trail of gun smoke, some people call it wisps. An airgun based on a centerfire or rimfire pistol or rifle is even more realistic looking with a smoking barrel, but high temperature is not conducive to proper functioning, especially with blowback action models. The higher PSI can be hard on the action and seals. At the other extreme, temperatures from 50 degrees to just above freezing, the CO2 is chilled, and already being cold to begin with, the PSI is lowered and performance drops rapidly along with velocity. In a very short time of exposure to freezing temperatures CO2 powered blowback action pistols stop working. Revolvers don’t fair much better after a few minutes. Whenever I have had to shoot tests outdoors in winter I keep the gun in a warm coat pocket between shooting sessions, or even pull the car nearby and keep the gun in the heated vehicle so the CO2 is at 70 degrees before taking it out to shoot. This extends my shooting time but the end result is still the same after a few minutes.
Cheating the elements
If you don’t have a basement or game room where you can set up a safe indoor shooting area of at least 21 feet from the target and provide a sufficient backstop and BB/Pellet trap, and you want to shoot an airgun, you are stuck outdoors when the summer temps soar above 90 or the winter cold drops the mercury to freezing. I think most people will wait until spring to shoot CO2 rather then trench through snow to set up a target, but there are a few stalwarts who like to try, others who need to use airguns for all-season training, and a few of us who do this for a living with airguns and cartridge guns alike, and need to shoot year round (deadlines care little for the weather). With airguns you can get away with more in the summer than the winter when everything comes to a stop if you are using CO2. There is, however, a way to cheat the winter temperature and win the cold war, don’t shoot CO2.
The Nitrogen Option
Leland Gas Technologies specializes in all areas of gas cylinders for commercial use as well as 12 gram CO2 cylinders for air pistols and 12 gram-sized Nitrogen cylinders for use with air pistols in cold weather. A Nitrogen cylinder for use in place of a 12 gram CO2 cylinder is the same size and loads identically. Nitrogen is already in a gaseous state, whereas CO2 begins in a liquid state and vaporizes (turns into a gas) when it is released by firing the gun, which opens a valve to dispense a measured amount of CO2 to propel the BB (or pellet). On blowback action models, a portion of the CO2 is also used to operate the slide mechanism. (This duplicates the recoil of the slide or bolt caused by expanding gasses in a cartridge-firing handgun or rifle).
Using Nitrogen instead of CO2 is the best option, but it does have its limitations. Leland offers different pressurizations for varying uses in a 15cc (12 gram-sized) cartridge for air pistols. They use a 1.8 gram fill to work with the same mechanisms and internal seals as 12 gram CO2 cartridges. Using more than 1.8 grams could damage the air pistol with too much pressure. The Nitrogen cylinder fill at 1.8 grams is 1700 PSI at up to 95 degrees. CO2 is 850 PSI at 70 degrees, however, pressure increases with the temperature. For a 15cc Nitrogen cartridge, 1700 PSI is at the lower end. A 15cc cylinder can be filled up to 2700 PSI with N2, but not for commercial air pistols.
For use in air pistols, the recommended fill of 1.8 grams in a 12 gram-sized cylinder will give you commensurately fewer total shots. The number of shots, according to Leland Gas Technologies, depends upon the design of the gun and its operating mechanism but it will still be less than with CO2.
While Nitrogen will not deliver the same total number of shots, it will work in temperatures where CO2 can’t, and Nitrogen cartridges are also not affected by higher temperatures in the 90 degree range. Thus the number of shots you get from a cartridge will be the same regardless of the ambient temperature. It all depends upon the gun. This is not to say that nitrogen PSI levels never fluctuate in severe temperatures, but the range of the 1.8 gram fill is an optimum 1700 PSI at up to 95 degrees. At an arctic low of -50 degrees, the PSI drops to 1200 and at +150 degrees, it increases to 1900 PSI; two temperature extremes few of us are apt to experience. (Leland’s graph for pressure and temperature actually goes all the way to +250 degrees).
Leland also makes high performance 12 gram CO2 cylinders under their Special Force Military Grade, which are used by the U.S. military for training guns and in paintball airguns. These are high end, precision filled CO2 cylinders that will give better performance and accuracy in air pistols. We’ll review them later this year. The Special Force CO2 cartridges come in a 12 pack for $9.60. Nitrogen, as you may suspect, is quite a bit more than the 80 cents each for a 12 gram Special Force CO2 cartridge. Nitrogen cartridges come in a 5-pack for $12.50. Leland does, however, have a price break for quantity purchases. Nitrogen gives you year round shooting capability, and for some, it is hard to put a price on that.
In Thursday’s Part 2 we’ll find out how well Nitrogen does in the winter freeze.