Depends on the carrier, and the personnel at screening/security.
We've been refused permission for carry-on. It could have gone in baggage. The irony, of course, is there's a couple of CO2 cartridges under every seat in the cabin, but we weren't allowed to bring another...
We even had a security supervisor tell us the cylinder could start a fire
Most airways and unions of airways allow to carry one cartrige on the pfd and one spare. Although carrying compreesed gasse is not allowed this is not the case for CO2 cartriges. Google for your carrier and CO2 cartriges and most probably you will find out that they are allowed. You better carry a printout of the document with you.
John Kretchmer wrote in his last book about how when he tried to take an inflatable life raft onto a plane shortly after 9/11, the airline insisted he remove the CO2. In the process, the raft inflated in the middle of the airport like a kids "bouncy house"!