Got it back together today
Bespoke mount to take HW 25mm seal. Ugly but works.
Fits piston and holds air indefinitely.
Shoots very well at 5 ft.lbs 8.3 gn Superdomes and 6 ft.lbs 7.3 gn Geco. which matches "F" rating
Very interesting/unusual, to me, internal specs.
Going to try groups tomorrow 'cos the few test shots today must be flukes!! We'll see.