 C02 is not a recommended propellant for the Promaster or any electropneumatic marker, as the cold liquid can destroy a solenoid valve.Instead, regulated High Pressure Air or Nitrogen systems are recommended although may be used if an Anti-siphon tube has been installed inside the bottle.Since the Promaster is able to reach firing rates of over 15 bit/s (30 bit/s is claimed by Indian Creek), it will operate best when used with a force-fed hopper such as Vlocity/Vlocity Jr, Halo, Empire B, Pulse, Fasta, and or a Dye Rotor.