It's time for the big one... help me out

[spudkpi]

I have built 4 cannons so far... 1 combustion and 3 pneumatics. I like pneumatics much much more for many reasons (more powerful, easier to build, cooler sound shen shot, etc. lol) but now I want to move to the next level in my spudding career and i'm considering building a massive pneumatic cannon. I want to build a co-axial cannon with a large 4'' chamber and cleanout cap but what i'm not sure of is what barrel size i should use to shoot normal spuds... whether it should be 1.5'' or 2''. I am also unsure of whether I should use a piston or a diaphragm and which would be easier. I have made one coaxial piston valve and it took me quite a while to get a good piston and good seal but now it works every time. I was going to use a modded sprinkler valve to relieve the pilot but I would like some input on the barrel size and whether or not to use a diaphragm or piston... I want to be able to shoot it right at 1/4 to 1/2 mile with a spud or other object, hopefully it's possible... i'm ready for the big one! Thanks.

[noname]

Just use a 10' length of 2" for the barrel and a 10' length of 4" for the chamber.

[spudkpi]

Ok is that a good C:B ratio? And what about the valve diaphragm or piston?

[noname]

C:B ratios don't matter very much with pneumatics, but this will be 3.5:1 or around that. Doesn't really matter if you do piston or diaphragm, that's your choice.

[spudkpi]

Well ive never made a diaphragm cannon before. Are they easier to get to seal than piston cannons? And which would be more efficient for a cannon this size?

[Torch]

I wouldnt go for a diaphragm. I tryed that once on a large scale gun like this and couldnt get it to seal and it was all set up right..From what i've read pistons can be much better then a disk of rubber. But dont hold me to that since I am still a noob.

[ProfessorAmadeus]

Yeah i like pistons more also. For some reason they are easier to make. It would be cool if you coul get a ten foot golfball barrel. That would go 1/4 of a mile.

[spudkpi]

Yea 10ft golf ball barrel would be very cool... are there any sch 40 pvc sizes that fit gold balls? I know that sleeved 2'' works but i dont exactly have good access to a table saw to cut the strip out to sleeve it...

[Torch]

Well, 1.5in SCH 40 pvc will fit golfballs with the shell removed. They will slide down but I would use wadding to seal it correctly.

[spudkpi]

Yea i dont want to have to bother with taking off the shells of the golf balls though thats too much of a hastle...i'm off to home depot to buy a 3'' coupler to start on the piston...

[runningawaypyro]

um how do you get the shells of golfballs?

[SpudStuff]

Cut it in an x shape then peel off the shell with pliers.

[Shrimphead]

Don't use a cleanout cap! They aren't pressure rated.

[runningawaypyro]

should i use a hacksaw>

[Infernal2]

You can.... And if you want an easy fix for cutting pipe I use a bosh 4" hand grinder with a masonry blade. You can also outfit a dremel with a 1" cutting disc. Then you simply use a chalk line to make two straight lines and cut them.