Made a gun of 40 mm caliber, used a piston valve. The gun works well at pressures up to 20 atm, no longer possible, because the rubber on the piston is torn.
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here is an approximate diagram of the valve. Used a coarse water filter.

A few days ago, I managed to make and test a piston valve with a caliber of 40 mm. I managed to make an exit into the barrel with a diameter of 14 mm. I pumped 50 atm into a cannon with a homemade pump.

Hello everyone. I made a new valve, it will work on CO2. How it looks inside can be seen in the diagram. The turner made the blue part for me on the machine, I soldered it inside the tee.

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I have a video with shooting from this rifle.