Soldato
Remove some of the steel adjuster shims inside the gun.
Or, have a coil or two cut off the mainspring. If you're going to do this, make sure the 'cut' is ground flat correctly, not just cut off square.
I hope they put some washers in as I hate grinding down mainsprings. Takes forever .
I've just tested my Cometa 300 and that was putting out 12.34ft/lb. I think this could be due to the fact its not been fired for a few years and was dieseling quite a bit on the 10 or so shots i fired. I have removed the washer from it and now its at 11.3 ft/lb.
I'll open the HW97 up tomorrow and have a look. IIRC its just a case of removing the trigger pins, then unscrewing the rear block.
Found a great site that has lots of different pellet weight on. Very useful
http://www.photosbykev.com/wordpress/2009/01/20/air-rifle-pellet-database/