Hi Davy
Old 85 is a fabulous gun.
They will do 15 ft lb all day if you push it.
You can sweeten them a little with a 10mm short stroke piston head but actually just a softish spring is enough really to make them shoot nicely at 11 ft lb.
Try 3-5mm of preload on yours on the back end - don't add any weight to the piston
Matty