Success!

Today I cut more off the front of the piston, and made an adapter for HW-seals. Piston plus eal now has the same length and stroke as the original osprey piston.
I had one of Maccaris 25mm HW-seals, that I had sized a bit too much Down for my HW30's. It swas till tight in the Osprey, so a bit of sizing was necessary. Still not free-falling, I like to let a seal bed in rather than beeing too loose.

Took the TP-sleeve out, reamed it a bit with a taper pin reamer to ensure it has a smooth inside surface, and cut entry tapers to bot ends of the sleeve.

Made up a steel tophat and washer to compensate for loss of piston weight from fitting the HW seal, piston plus tophat and washer weighs 210grams.

I have been using Maccaris HW50s/HW99 spring, but added some more preload now, guided by a delrin rear guide.

The gun now does 550fps with an extreme spred of 7fps over 10 shots, with Defiant vintage .22 pellets- that should be 9.7fpe.

Now its time to see what this gun can do- I'm happy with its performance, it just needs to be shot!