If you don't see how it works or what I intend this device to do this series of events might help
1. pin is pulled via tripwire
2. piston travels downwards thus, pushing against the spigot and accelerating the "mine" into the air
3. the piston is caught and the air pressure begins to force the projectile out of the barrel (hopefully delayed until the vertex of the trajectory is reached by the detents)
My alternated trigger design is similar to a gate latch bolted to the bottom plate and a notch on the piston shaft.
Note: I do not intend to castrate anybody
