A simple rubber band gun i made for the kids out of a piece of 19mm pvc electrical pipe ,some wire and rubber bands.
It can also shoot multiple rubber bands at the same time.
I made an extension piece which i can put on if i need more power.
Or leave it straight and make a wooden handle and put that on.
i made the holes 4mm.
the 4mm hole in the top of the gun might need some enlarging.
put on the rubber band for the trigger.