I haven't described the test very well .
Effectively I've attached an air line at 100psi to the muzzle.
With the probe closed , firing valve is deliberately in the closed position by resting against the dry fire pin .
Thus the pressurised. Areas are :
Barrel , probe orifice, transfer port, and the small chamber to the hammer side of the firing valve.
The valve is closed to eliminate the reg from the test . As all I want to test is the valve stem .
The barrel seals and probe seal are all fine. No air can be heard escaping and a further test by dusting with talcum powder and firing a pellet confirm this.
The only escape route for the compressed air is the unsealed valve stem .
The gauge is academic really and just gives a value to the leak.
I don't having the firing valve in the open position will make any difference. The amount of lift to the valve upon striking with the hammer, I would say is a tiny amount. Max 0.5 mm I'll try and measure but it is tiny compared to the amount of stem in the drilling of. The action