The matter of CO2 pressure may seem intimidating at first, but knowing the basics makes it easier to understand matters such as velocity and how many shots per cartridge. CO2 is carbon dioxide compressed in a cylinder tank capable of powering an airgun. This substance is a gas capable of forming a liquid when mechanically compressed. This unique nature allows the substance to achieve a certain pressure of at least 852.8 psi when combined with an ideal temperature of 70 degrees Fahrenheit. The ideal psi for airguns is a minimum of 852.8 to 900 psi. The matter of psi relates to velocity in terms of temperature and whether the cartridge is mostly liquid or gas when fired.
For many airgun enthusiasts, the matter of CO2 seems more complicated than it is in terms of pressure and how it all works. While you may know you need it for your airgun, it may be something to never really think about beyond loading a new cartridge in your favorite airgun. When it comes to CO2 cartridge pressure, there are a few things worth knowing. Lets take a closer look at this interesting element of airgunning and all the basics you need to know.
Before we get into the matter of PSI, we need to cover a few useful basics. What exactly is CO2? CO2 is carbon dioxide that is compressed into a small, usually cylinder, tank or cartridge that can power an airgun when it fires the pellet. It has been in use for this purpose since at least the 1870s when a French man named Paul Giffard first used it in his gallery guns and sold them to the public. This was such a novelty in these days that people had to send their cylinders to special filling stations to have the CO2 replenished.
In the 1940s, Crosman was in the process of expanding shooting in general to something of a fun hobby and entertainment. They created indoor ranges for people to experience the fun of shooting in a more accessible manner. They also made the 4 ounce CO2 bottles which would become a collector item and further fuel the publics interest in CO2 airguns. While the early guns of Crosman werent sold to the general public, Benjamin would pick up where they left off with their sparklets and Crosman would eventually get in on selling this type of gun to the public in the 1950s. Since then, CO2 has become a common standard in the airgun industry for good reason. It offers an easy way to power the airgun with a mess-free method that is also readily accessible at any airgun retailer.
CO2 Cartridge Pressure
Now that you know what it is and its origins, we can get into pressure and how many shots you get per cylinder. A lot of people are confused on CO2 cartridge psi and how it works. It is important to keep in mind that temperature and pressure work together to create the power behind the shot. CO2 is a gas substance at a temperature above 69.9 degrees Fahrenheit and a minimum of 60.4 pounds per square inch. CO2 is a complex substance with the ability to change from a solid to a gas without becoming liquid (unless through mechanical compression). The pressure or psi is a result of the temperature in terms of the gas and is not created by the use of mechanical compression. This means that you mechanically compress CO2 in the gas state it will be converted to liquid when the right pressure is reached. The pressure will then remain constant until all the liquid is gone and this is why a CO2 powered gun will not lose velocity until all the liquid is gone to the point it is running solely on gas.
The general standard is that when CO2 reaches 70 degrees Fahrenheit, the gas obtains a pressure of around 852.8 psi when contained in the cylinder or vessel. If there is more CO2 in the cylinder, it will then be converted into a liquid form. This means that the cartridge is a pressurized gas above a liquid when at room temperature. When the airgun is fired, it releases some of the gas and converts some of the remaining liquid to gas to fill the remaining space until the psi is equalized for the temperature. So, what is the pressure in a CO2 cartridge? It will depend on the temperature, but the minimum is between 852.8 and 900 to get enough power behind the pellet to reach the specified velocity or FPS.
It is also worth noting when looking at CO2 psi that it is a refrigerant gas which means it cools when it expands. This means that if you fire your CO2 gun in rapid succession, the gas in the cylinder will cool and lose pressure. This will reduce the psi and lead to a slight velocity decrease. This is why most airgunners dont do rapid firing with CO2 action when trying to hit a mark or target for accuracy training. The good news is that CO2 doesnt take all that long to go back to the right temperature, usually around 12-15 seconds between shots, or less, depending on the ambient temperature. Apart from temperature considerations, CO2 is very consistent and will produce fairly regular velocities as long as the CO2 is still liquid.
How many shots you get from a CO2 vessel will depend on how much gas is used to create the velocity in the shot. A general rule of thumb is that a CO2 powered pistol will give anywhere from 50 to 100 shots per vessel while a rifle will give around 40 to 50 shots per vessel.
CO2 and Velocity
As mentioned before, CO2 and velocity are related. As you reach the end of CO2 in the cartridge, the psi will start to drop, and you may lose a bit of velocity as a result. Velocity may also be increased when shooting in warmer temperatures, and that means your velocity will also decrease below the 852-900 psi range in cooler temperatures. CO2 guns should not be shot in temperatures much below 60 degrees Fahrenheit, or you risk the gun jamming or the projectile getting stuck in the barrel. It is important to keep in mind that while psi is a factor in achieving velocity, there are other outside influences that may be getting in the way of you hitting that velocity aside from the cartridge.
In conclusion, CO2 is a great way to power an airgun without a lot of hassle. As long as you have a basic understanding of what this substance is and how it operates, you will be able to enjoy years of shooting fun using your favorite CO2 powered air pistol or rifle.