SPECS
Barrel: 650mm of 20mm electrical conduit, its really loose 1mm each side

ammo capacity: one 20 round mag and two 10 round clips. all spring fed, homemade springs.
Valve:1/2'' festo qev, 10mm seat.
Pilot Valve: 1/8'' pantball slide valve.
Chamber: 10cm of 3/4'' galvanized pipe. small but 600psi makes up for it

Operating pressure: 200-600 psi, with my 1l tank i get 20 really good shots 10good shots, then i refill it.
Reload mech: homemade air cylinder to cycle ammo, the receiver is two brass tees with a peace of 20mm copper pipe soldered in it.
thanks to Poland_spud and jsr.