A key area where CO2 circuits differ from industrial or garage pneumatics is that they run much colder. When you first turn on the CO2 supply, the liquid CO2 boils at -57°C, which would make some lubricants turn into a wax, actually impeding the actions of valves, etc. Robots often end up internally like a scene from the South Pole after a bout, from all the frozen atmospheric moisture that collects on the pipework. So the recommendation of using paintball oil (paintball guns often run on CO2) or similar, is a sound one. One thing you will have to watch out for is the regulator or other moving parts in the CO2 circuit icing up, either stopping the weapon from working, or causing an unexpected rise in circuit pressure (that has happened to us before).

We have a car that runs on LPG, which has an evaporator that is heated by the radiator water to ensure that the LPG actually turns into a gas rather than entering the engine as a near-cryogenic liquid. If we had more time and resources, it would be tempting to build a heat exchanger round the motors to use their waste heat to warm up the CO2 to overcome the problems described above.