For anyone interested I attached a schematic for a variable speed trigger controller. Range is 18ms - 1200ms. Ignore the pc board diagram. That was for my benefit. A friend designed and built it for me. I'll try to answer questions, just don't get to techy.

Charged the water cannon today with water and blew the 90 degree elbow apart on my 36" barrel. I believe, and maybe someone knows the answer, that since I only filled it half way with water that the sudden change from 4" to 1-1/2" and the headspace above water is the reason. I will fix and try again...

Yeah the recoil was my big concern. I may have to really secure everything.

Whoa! That's a cannon

Has anyone made a compressed air cannon using water as the projectile? I recently built an air cannon and plan to use a length of 16" 4" pvc with 1-1/2" reducer as the end piece on a 96" connection of 1-1/2" pipe connected to tank. I'm using a 3/4" QEV. I roughly modeled with GGDT and got a 1000 ft ...