Somebody posted a thread on this at SSC
here.
It can certainly be done, but only if you have the resources and are better at it than we are. A magazine may not be advisable and a hopper may be prefered, but you'll have to figure that all out if you want to make one.
@iSoaker, I don't know about you, but I wouldn't have any problems whatsoever with an automatic launcher. It would be an overpowered weapon (unless it can't be reloaded easily) but I wouldn't mind having one. The
real reasons that many warriors don't use water balloons these days (anybody with any decency will clean up their balloons and they are much more likely to be a hazard to animals than children) is because they are simply not as practical as blasters. Currently, my group only uses them for suppression and getting kills with them is very, very rare.