This is a small spring-loaded missile launcher based on my printable spring design
The design doesn't have a trigger, there's a small hole in the back of the launcher you can tie any thread or wire to and pull it down to fire (the reason is that I plan to incorporate this into a larger design that will trigger the launcher)
I printed it in PATG, no supports, no infill, 3 shells, 1mm top and bottom
Spring designed in OpenSCAD, the launcher designed in SketchUp, STL fixed with Microsoft 3D Builder.
I sliced it in Cura and printed on my Robo3D R1+