CO2 Basics 

The modern CO2 tank is the staple of recballers and paintball fields across the United States.  The extensive use of CO2 along with the increased appearance of fill stations are retail outlets, along with its reasonable cost, makes it a choice for thousands of players. Understanding CO2 is essential to understanding your marker, potential upgrades, and your own safety when playing.

Remember, CO2 is a liquid and a gas, and your tank might be filled with a combination of the two at any given time.  Please play responsibly and use a chronograph for casual play. CO2's proneness to fluctuate in velocity makes it extremely important that you keep marker speeds in check!  When liquid CO2 enters the valve of your paintball marker, it can cause erratic velocity spikes and damage o-rings. This is mostly characterized by pieces of CO2 "ice" coming out of the paintball gun. This "ice" does not melt, but will sublimate (turn into a gaseous state immediately) and is very cold.

How do you avoid getting liquid into the marker? Many blowback guns come with angled ASAs to tip the marker backwards and help keep CO2 from going through the airline into the marker. You can take this even farther by holding your paintball marker upside down, with the barrel pointing upwards. This keeps the liquid at the rear of the tank. An anti-siphon tube can be installed, which helps to only allow air into your marker. An expansion chamber or regulator can be purchased and installed on your marker as well.

What do you do if CO2 has entered the marker?  Try holding it upside down and point your barrel toward the sky, at a sharp angle.  Fire your paintball gun around 10 times until the visible white jets decrease and you stop seeing "snow" exiting your barrel.  Then just carry your marker upside down to prevent more CO2 from entering.  You want to make this a practice, especially when playing "outlaw" ball.  Since chronographs are (unfortunately) often overlooked, liquid CO2 usually raises the velocity of the paintball substantially.  A paintball marker chronographed with air at around 290 Feet Per Second could chrono in at 315 when shooting liquid CO2.

'Pin Valve Tanks' are the mainstay of the paintball industry.  If you've got a CO2 tank, this is what you've got.  They are simple, easy to maintain, quick to fill, and very common.  They can be equipped with anti siphon tubes and on/off dials.  They also come in a variety of shapes and sizes.  Unlike HPA tanks whose size is measured on cubic inches of space and pounds per square inch the tank can hold, a CO2 tank's size is referred to by the amount of CO2 (the combination of liquid and air) that the tank is designed to hold.  The smallest refillable CO2 cylinder available for paintball use holds 30 grams.  The largest common tanks hold around 20 ounces.  As a result, some tanks that hold the same amount of CO2 can be different sizes.  For example, some 9 ounce CO2 tanks are long and narrow, while others look like smaller versions of 12 ounce tanks in the interest of comfort.

When you go to get your tank filled, remember that the fill operator cannot "top off" your tank - its entire contents need to be dumped so that the tank is chilled, and then it is filled. (Technically, a CO2 tank can be “topped off” if it can be frozen and if the exact weight of the tank is known but this would take time and is impractical).  If you haven't played a lot of games with a tank, use up more of the air it contains before getting a fill.  However if you're not sure, it's always best to fill the CO2 tank completely.

Which type of tank you want to buy is up to you.  Keep in mind the length, weight, and approximately how many shots you can get out of your tank when you look to purchase a CO2 or HPA tank.  There's no way to tell how many shots you can get off any given tank, because of tons of factors (the type of paintball gun, the amount the fill operator filled the tank to, outside temperature, secondary regulation) but here are a few LOOSE generalizations.

4 Ounce - 150 to 200 shots
9 Ounce - 450 to 500 shots
12 Ounce - 500 to 600 shots
20 ounce - 600 to 650 shots

Be extremely careful when buying used CO2 tanks! A tank might appear fine on the outside but the internal o-rings could be damaged. Certain CO2 tanks also must go through hydrotesting periodically, an essential safety procedure that tests the integrity of your tank. Using an old tank and trying to "risk it" might seem economical, but safety is not something that can be purchased.

Paintball is a very safe sport when the rules and regulations of the game and equipment are adhered to.  A butcher's cleaver could maim or kill, but he knows how to responsibly use it for its purpose.  You have the same responsibility to understand and exercise safety with your CO2 or HPA tank.  If your tank is larger than 9 ounces, it will need to be hydrotested periodically. Hydrotesting ensures that the integrity of your CO2 tank has stayed the same and that it can still be filled. 

However, this service is reasonably expensive and it might be more economical to simply buy a new tank.  Do not try to fill or use any tanks that are damaged, including deep scratches and gauges.  Most importantly, pay attention when unscrewing your CO2 tank from your gun or remote line and always allow a professional to install new parts to your tank.  If you ever notice that the tank (black part) itself is unscrewing from the valve (brass part), STOP IMMEDIATELY.  Put the paintball marker down and inform a field staff member immediately.  Unscrewing a pressurized CO2 tank from the valve can create, essentially, a small missle.  There have unfortunately been accidents where tanks have come unscrewed from valves and killed people.  These incidents are extremely rare, but vigilance on the part of players can potentially save lives.

Your tank is an important investment - take care of it!  Replace the tank o-ring as soon as you notice any frayed rubber, cracks, or warping.  Lightly oil your o-ring as basic maintenance.  Buying a thread-saver cap which screws onto the top of the tank is also a good way of keeping your threads safe.  Never force a tank in or out of a gun: crossthreading your tank into your ASA will be a costly repair.  Do not keep your tank next to a boiler or heater - the CO2 can expand in the tank when exposed to heat and could cause a problem as well as a safety hazard.  Make sure that any tank that has had something installed on it (like anti siphon tubes, on/off switches, and new valves) is loc-tited and sits for at least one day before being used, as the thread locking agent has to set. 

A small sticker on part of your tank may be helpful in telling which tank is yours if you keep your tank among friends, but do not put any scratches into the tank.  Keep a supply of bottle o-rings and gun oil and replace your tank o-ring whenever it appears cracked or damaged.  Small tank leaks can sometimes be fixed with a bit of oil spread over the o-ring or into the pin valve.Despite the fact that HPA is continuing to push into the recball market, CO2 is still one of the most comfortable and practical air systems for blowback and pump marker users. Understanding your CO2 tank will save you money and time, giving you more time to focus on what’s important – playing the game!