I've recently acquired one, and was planning on visiting a local site that uses CO2 only - will it be safe to use with CO2? I can't see any problem myself, but thought it best to double check...
Just be careful now the weather is starting to change, that the temperature of the tank dosen't get too cold, tend to get psi fluctuations in cold weather with CO2, effecting cockers quite a bit in my experience.
By the way - some pumps like the early Sterling's were designed to run on liquid CO2 full time. They had syphon dip tubes installed in the bottles to ensure it always pulled liquid not gas. Mind you it was like shooting a fire extinguisher in cold weather. After a few shots the CO2 plume totally blocked your view and also gave your position away on the field. Another plus point for shooting air.