Minimal piston length

[psycix]

Fair enough, the biggest pneumatic I ever made was 3/4" calibre so I guess I live in a world with smaller limits

I like smaller launchers, you use less material (and waste less if you have to throw it away and start over, a not unheard of eventuality with epoxy) so it works out cheaper, they're easier to store and if you up the pressure, the power is still impressive. If I lived in a rural area though, it would be large calibre beasts all the way

I dont live in a rural area, I live in a decent sized village.
But when I am going to fire I just fire in my backyard (when the evil neighbour on the other side of the street is not at home) or I just go out of the village.