For over fifteen years my friend Jay and I have exchange trapped presents at Christmas. When I say trapped I mean it in the classic Circle of Death game style — if you open the present carelessly a buzzer will sound or explosive cap will trigger.
I usually focus on making it difficult to find and disarm a simple explosive-cap trap, but this year I wanted to change things up a bit and focus on the effect itself. In particular, I wanted to make a box trap that would shoot darts out in all directions, machine-gun style. It had to be completely mechanical (what can I say, I like the style better), and had to be stable enough to ship through the mail without going off or getting jammed. After many attempts I landed on this rather elegant sprung-hammer design (click for video and construction notes).