SpudFiles

As you can see, my cannon is almost ready in principle and I have taken some shots and worked fine pressures 1-2bar with blowgun as pilot valve and pilot channels ID was 5mm, but valve didnt open in higher pressures.
So, next I took the blowgun away.Then I tested could it open if I put my rubberglove on it and then fast take it off from the hole. Well,it worked with pressures 1-5bar but didnt opened in higher pressures.I think that I could fix the problem by drilling the hole 5mm---->10mm and put 1/2" ballvalve to it?(sorry for bad english)

Does sound like a pilot problem, the 1/2" ball valve should do it and as you already mentioned, making the hole larger.

Could we see your piston?

I love the finish, pity the barrel-chamber bracket looks so "new" as it jars with the weathered look of the copper. Also like the crushed tube method of closing off the chamber

did you try modding the blowgun?
detail are in this howto
http://www.spudfiles.com/forums/how-to- ... t7038.html

I will add this to the "Cannons" when I get my rest parts and then I tell you more details