Well instead of cramming enough cabbage and legumes into a revolver-sized weapon, I wish we had some sort of propellant that would expel enough gas to propel a bullet. If only such a substance existed that we could use in very little quantity that would accomplish that task.
Oh wait, we do... Gunpowder. I appreciate the idea, and sorry if I've sounded like a jerk, but there's a reason we don't launch projectiles with the gas from decomposing produce.
EDIT: That is if, of course, you were serious about the cabbage and legumes idea. Oh wait, you just meant the gas that they cause people to have. :facepalm:
I must have been thinking of some other mythbusters stunt.