3" piston coaxial help

[singularity]

well im making a coaxial pneumatic with a 3" camber and a 1" barrel. that would mean i need a 3" piston. my idea was to get a 2" cap and a 2" plug glue them together and use them as the back bone to a 3" piston, then i would put them in a section of 3" pipe and dump some hot glue in to make the piston. now i have a question; would this work? or would the piston be to long?

cannon length - 40 inches
camber diameter - 3 inches
barrel diameter - 1 inch
piston coaxial

ps- how should i support the barrel inside of the chamber?

[noname]

Tye piston will work fine, just leave enough room for it to slide back.
As for the barrel support, just use pieces of pipe, for that gun, I'd use 3/4" or 1" PVC, not sure which.