There are tons of airsoft artillery options that work on the same principle as a pumpkin gun. Go that route; having a valve that opens fast is key. It has to dump the pressure as soon as you pull the lever.
If grudge's take is right and then yeah way more problems. The Co2 will not toss out that football with any serious energy. It'll just waste itself equalizing pressure and then you'll have to clear the breech for he next shot.
Airsoft, where nothing is hurt but feelings.