I was looking at a PVC rocket (not a real rocket, just a mock up of one to be fired from a replica WWII bazooka) on this forum (i cant find the link), it has a PVC cap, a length of PVC pipe and on the then it has been heated on the end and put on a funnel to make the end bigger.
This got me thinking, and drawing 8)
I designed this
Yes, yes, its something that I drew on paper, then took a picture of it and used photobucket to edit it
Its a PVC rocket with an "electronic barrel leaving switch" (EBLS), when it fired from the barrel of a gun, a wood dowel will pop out and allowing the spring metal to touch the contact point. This could be used for a variety of things, turning on a light inside the rocket or whatever you want. I know that there are limit switches that do this but this is for people who want to make thier own.