As I said, this is basically a piston. It uses inertia to fling it's contents out of the pipe. Plant the trip mine at roughly a forty-five degree angle. String out the tripwire and plant the stake on the opposite side of the path. Push the mechanism down with the plunger and insert the pin. Make sure as little of the pin as possible is holding the plug in place. Then pour the appropriate amount of BBs and powder into the trip mine.
View the video below to see the trip mine in action.
YouTube's quality is horrible, I'm using Metacafe instead.This is the detonation of the trip mine at 1200 frames per second: