Reducing pilot volume and piston size

[Biopyro]

Is there anything I can do apart from designing a track? I've seen other people use similar pistons, but never using a track. The diagram isn't to scale, but would making the discs thicker help?
I may just drill out the centre of the piston so it's a cup shape.

[sgort87]

If you can get the back end to be about a half inch long with a close tolerance to the wall, it should work, but if it's too thin and/or the tolerance isn't right then it will jam up on you like you have pictured.

[Ragnarok]

A simple way of doing it would be to use three discs on the bolt, so there are always two supported by the pilot volume walls. It works fine when I do it, and my sealing faces are almost invariably right near the front edge of the tee (to help flow and avoid excess dead volume).

Now, like I've said before, minimum pilot volume isn't always the best option, because if the piston's movement sweeps out a large percentage of the pilot volume, then it'll cause noticeable adiabatic heating, which may actually slow pilot opening.
However, with a decent pilot valve and some "dead" pilot volume (where the piston either can't move into, or piston travel past what's needed), the problem shouldn't be a major issue.

Still, if trying to design a cannon where you're trying to squeeze every last drop of power you can out of it, one might want to look into such things.