I know 16mm (0.62") marbles are approx 5g each if that helps.

I did, the hole was drilled out to 5mm (1/5") which has proven to be more than enough. The reason I placed the trigger over the existing solenoid hole was to avoid having to remove the guide rod. Despite what a few people have said I believe it is necessary to ensure the diaphragm seats properly.

Cheers windshrike, I actually upgraded it a while ago but never got up to loading new pics. The trigger mechanism I was using caused the barrel to move a lot making shots unpredictable and inaccurate. To avoid this I went down the much trodden path of a sprinkler valve and window washer. The power ...

I understand what you are trying to do but don't understand why? Air would have to pass through all the small holes before going down the barrel, this would severely hurt the performance. Also it would only work if the "cover/holder" fit snugly inside the T/chamber (depending on whether it's a ...

No one seems to have pointed out yet that 350m/s is faster than the speed of sound, so you may have some problems there, 250m/s is a much more reasonable speed to aim for and still fairly impressive.

1) increasing chamber size never hurts, but may not help depending on the size of the barrel and chamber initially.
2) shrinking the chamber will most likely hurt performance, especially if you're decreasing it below ideal C:B ratio.
3) if the barrel is increased too much it will hurt performance ...

Are you sure you're attaching the chamber to the right end of the sprinkler valve? The arrow needs to point towards the barrel for an inline or away from it if you're using it as a pilot.

I had a piston fail after just a few shots. It used to be made from a 25mm end cap surrounded with a 32mm internal sleeve and a bit of neoprene on the front. The pressure from the 150psi pushing it against a 15mm barrel was enough to break it. I replaced it with a piston made from a bolt a few nuts ...

If PVC cement comes into contact with the chamber it will weaken it. the cement is a solvent which means it actually dissolves the PVC and allows it to set again which is how it manages such strong bonds. Sorry for the off topic.

I've only had two minor incidents, one when shooting a metal bucket about 8m away with my marble cannon where I missed the bucket and hit a 2x4 behind it, the ricochet missed my head by about an inch, gave me one hell of a fright.

The second I had just modified my marble cannon with a new, better ...

Yes, but a homemade spark plug that can be made to any size you desire.

If you used the sleeving approach you might have trouble keeping everything in place during combustion. You'd probably have more luck drilling a small hole through the center of a bolt and passing a length of HV wire though the hole then as you say, ground the chamber. Check out http://www ...

I stand corrected. I was making an assumption based on the fact that the PVC is generally rated for 160psi and thats assuming the pressure is on the inside of the pipe. That being said, 160psi leaves a fairly large safety margin and I can't really see why the rating would be any less for external ...

Things just got very interesting. I eventually got around to replacing the piston I had thrown together to replace the broken one with a proper Neoprene piston. The last piston was made of a high density foam which leaked a little and opened slowly, the neoprene however, with a small amount of ...

It depends on the configuration of the gun. If you're making a coaxial I wouldn't take it to 200psi with pvc or the barrel could quite easily be destroyed. Not really a safety concern because it will collapse inwards but a waste of money.