just upgraded my leather HW35 to synthetic...

[Shed tuner]

What stroke length can be achieved without adjusting the slot in the piston?
I'm a bit concerned about weakening both the piston skirt and the piston rod attachment.

you need to measure your own rifle mate, there's a bit of variation. mine was around 6mm. just see how much clearance you have from rear edge of cocking shoe, to the piston cocking slot rear edge. Whatever that is, you can increase the stroke by (allowing 2mm for clearance) without any further mods. Then measure the height of an hw 80 seal, compared with the leather nose, and then work out how much metal you need to remove from the piston for it to add up.

Piston still has plenty of engagement with the rod... if worried, just buy a new synth HW piston/seal.

[evert]

Thanks! Measuring is probably (like always) a good idea before I start cutting metal! Just curios to know what other people have found and done.
I've already converted to a synthetic seal, and the rifle is a transitional 1980 gun with a small transfer port.
Buying a new piston is not an option right now, since I've already overspent on airgun parts lately