I know that some will say it is a bad thing, but you can pour some water into the breechplug and down the barrel. Let set for short time (say 15 minutes) then try to remove plug. Does not do anything to help the breech plug come out, but it does wet the powder sothat there is less chance of ignition.
Personally, I have found the CO2 things to be absolutely worthless- don't waste your money. Used up TWO cylinders and still did not expell the charge. Ended up wetting the charge, removing the plug, then pushing the bullet out with the ramrod.
CHILDREN ARE OUR FUTURE FOR TOMORROW. INVEST IN TOMORROW BY TAKING A CHILD HUNTING OR FISHING TODAY.