Bringing this back to the surface again, as I finally have som motivation to work on airguns again...

The standard UK (6fpe?) stack seems to be:
(((())))((

A suggested 12fpe stack is:
))((()))((

Can anyone suggest a stack that would work in between 6 and 12 fpe?
If I remember correctly there was 12 belleville washers in mine, which was bought second hand and could be a swedish 10joule version.