Cannon name: "Chappy" cannon made by Sam Tex
Type of gun: Pneumatic
Chamber size: 5.4 liter (90 mm diameter)
Barrel size: 53mm bore, 1.2meter length
Gas source: Bike pump ( boy, what a work out!!)
Valve: Homemade 77mm piston actuated by 3/4" ballvalve
This enormous ( I believe it to be Europe's biggest

It has a 5.4 liter reservoir made from 90 mm pressure-rated PVC.
It's a B! tch to find pressure rated PVC here in Holland.
It has no manometer because our bikepump has a very accurate one.
The piston is made from a bolt and washers, some 8 mm neoprene ( also hard to find!) some MDF, and some very snug fitting perspex rings.
No need for O-rings.
It actuates like a mother, even at low pressures.