This weekend my oldest son and I built ten marshmallow guns (that shoot mini-marshmallows). The design is similar to that shown at http://www.instructables.com/id/Marshmallow-Shooter/.
The parts are all 1/2 inch PVC (and all unthreaded).
For one blaster:
- caps (2)
- elbows (2)
- tee joints (2)
- tube 12″
- tube 6″
- tube 3″ (5)
For the tubes, we purchased three ten-foot tubes, which was enough for 10 guns.
The only tool we purchased was this BrassCraft 1-1/4-in PVC Cutter, which worked great and can be used indefinitely.
Originally, I was loading the mini-marshmallow in the barrel, which was a mistake. The marshmallow should be loaded in the mouthpiece. Despite my initial skepticism, this is by far the best way to load the marshmallow.