If I get a .177" TX to play with it may be worth sleeving the transfer port down to up the SCR and then increasing the spring preload.
If that doesn't work little machining to increase the stroke and reduce the port length wouldn't be out of the Question.
All good clean fun though Jon.
All the best Mick
You could always lighten that piston , by losing the skirt.
I am sure Slinger would agree with me here, at Quigley Hollow, we never want to lose the skirt.......