Mo - thanks for the baby best wishes. Although "Doppio" would gain him respect in *some* circles, we opted against it
Instead, his name is Noah.
I'll pull the piston out soon and measure it. But regarding the spring forces, using the data Mo posted, if you take the gap of 10.3mm and the wire diameter of 7.09mm then the pitch is about 17.4mm so there should be 7.6 coils in the spring. The calculator at this website:
takes the number of *active* coils, which I figured was 7 because at the ends of the spring they are ground down and thus not really contributing to the load, and the other info about the spring geometry and spits out these parameters:
K = 219lbf/in
max load is 587lbs.
I realize this is not metric, but no matter how much I talk millimeters I still think in psi for pressure! What we need to know now is the compressed length of the spring at the start of the stroke and the end. There should be a preload on the spring so that when the shot ends the spring force will not be zero. Also we need to know the piston diameter. I'll get on that