Summary

A pump-action pneumatic crossbow that shoots foam projectiles or mini-marshmallows with bow power. This is an old design, latest iteration can be found here:

http://www.thingiverse.com/thing:672304

Instructions

Make sure you save the assembly diagrams from the gallery--you may need them to put this together. Machining drawings are provided in .PDF format for all of the cut parts, and many of the printed parts as well if you'd like to produce a machined equivalent.

If you compare the photograph and the schematic, you'll see that there have been substantial revisions to the plumbing. The photographed blaster has an internal check valve that is much more difficult to make, and impossible to disable

All .stl files are in inches, so most printers / slicers will need to scale by 2540%. Holes sizes and some other geometry has been tweaked to produce parts that fit the PVC pipes on my 0.5 nozzle Prusa, printing ABS. You may need to alter these to get the right fit.

_BullPAC25.stp is the entire assembly, including printed and non-printed parts, which may help you do that depending on your modelling software.

For the bow, getting tubes to fit together like this is a non trivial task. Getting 1/2" CPVC inside 1/2" EMT conduit is always a hammer fit, and that's OK, but the 1/2" Thinwall PVC and the 3/4" CPVC have to slide over the aforementioned EMT conduit easily. The EMT conduit seems not to vary so much, so I would focus on finding thinwall 1/2" PVC and 3/4" CPVC that slides easily over the EMT.

Bullpup Toy Crossbow