Then I have tested different cup seals. After 4 or 6 tests the optimal shape looks be such like:
- minimal OD (to fit in the existing valve nut) and rounded back edges, with only minimal seating space for the spring
And it has such like final effect:
- 47 consistent shoots with avelerage muzzle velocity 257 fps, and total 469 Joules of KE in 50 shoots per 12g.
...bolt modification should follow. Im Heading for 500+ Joules / 12g.