The problem with CO2 is it can convert from gas to liquid and visa versa very easily; this is a problem for paintball players and their equipment.  CO2 is very sensitive to temperature changes.  When rapid shooting, it’s common for CO2 tanks to ‘freeze up’.  Next you will notice the velocity of your shots drop off and starts becoming inconsistent.  When you rapid fire your paintball gun you are use a large amount of C02 very quickly.  Your tank gets cold because the liquid C02 inside is changing into gas to replace the C02 used during rapid firing.  This change from liquid to gas is called a ‘phase change’.  When you fire your gun (with a chilled tank), you are releasing less C02 than if the tank was warm. 

There are also problems if your CO2 tank gets too hot; if you left your gun and tank in the sun for example.  If your tank approaches 89 degrees (F) all of the liquid in the tank will expand and the gas has nowhere to go.  Hopefully you have the right rupture disk in your tank because at this point only two things can happen.  Either your tank's rupture disk will burst preventing your tank from rupturing or your velocity will rise to very dangerous levels.  Moral of the story.... consider an hpa tank or keep your CO2 tank a constant temperature.