Last year I decided to make my own Christmas bonbons instead of forking out money for what is essentially rubbish. The toy component of my bonbon was this rubber band gun.
The gun was designed to dismantle in order to fit inside the cardboard tube and when assembled, be operable by my then 18 month old son. In keeping with the simple theme, it's a manual-load, single fire affair.
The gun is assembled trigger first into the body from the underside and then the handle to keep it together.
It's designed to work with small No.14 (50x1.5mm) rubber bands.
This rubber band gun was design to be printed on a SLA printer, so the clearances between parts may not suit FDM printing. Let me know if you attempt to print this with an FDM printer and the clearances need to be adjusted.