the push rod on the right only uses an oring on a brass end with no cup seal? How does it force all the air in? It seems like you could pump a stroke in but not get it to return due to suction issue? Explain.
What did you make the green cup seal out of? How is it secured to the rod?
Interesting results. At 3 pumps how did the fps vary in a 5 shot string? How was the pump effort at 8 and 10 pumps? What kind of power could you get?