This is a list of two materials and their pros and cons

ABS

Pros______________________Cons

-Strong____________________-Not pressure Rated

-Durable

-Doesn't crack in cold weather

-Chemical Resistant

PVC

Pros___________________________Cons

-Pressure Rated_____________________-Weak in cold weather

-Easy to find________________________-Non-chemical-resistant

My Personal choice for a pneumatic cannon is PVC because it is pressure rated and easy to find. You will be dealing with high air pressures in this type of connon so you will need that rating. Abs is hard to find pressure rated, and you won't need a chemical resistant pneumatic gun. PVC is great if you don't use this in cold weather.