Hi all, thank you for your thoughts and advice. I was a good 8' away from the chrono, Cleaned and de- burred and polished everything. Got a set of seals and bits from America, the biggest thing that was out by a mile was the shuttle alinement with the barrel, so the pellet had to almost turn a corner to enter the barrel. Sorted by a tweek of the cam, 2 adjustable wrenches and twist very carefully, when the hole in the shuttle lines up with the barrel - job done. The hammer was, shall we say, a generous fit and the 'O' ring flush with the surface so not actually doing anything at all.
Was thinking of getting another and seeing just how it would 'go', not to be used outside of course.
Thank you.
Cheers.
Geoff.