When I was a kid, you saw ads for a BB sub machine gun in all the gun rags that used canned Freon for recharging car AC systems. Haven't seen one of the ads in years, I assume they are out of production now, but as a kid, I always wanted one and couldn't convince Dad I needed it bad enough.
Where does a guy get such a thing now? Sounds like it would be a lot of good, clean fun to blast soda cans with.