I spoke to one of my local rfd's (geof wilsons in Carlisle) who I know quite well. He had done some repair work on a tracker, he fitted an OX spring but didn't have the correct seal to hand.

Instead he found a diaphragm seal that would fit and he reckons when he chronyed it was shooting way over 13ft/lbs. He ended up removing the piston weight to drop it just under 12 ft/lbs. Since then he has been asked by a couple of other customers who own trackers to do their guns.

Certainly sounds like a big power jump, anyone else tried similar in a Tracker?