Hi Monkey
I have a hw77 and it is a very capable gun, I would suggest taking it to your local gun shop and asking them if they would crono it for you if you have got concerns about the power just to make sure that it is pushing between 11&12 ftlbS if it does turn out that your gun is down on power dont worry you can get a new good quality spring for about £20 but if you fit it your self make sure you get the power tested after as you can make your gun over the legal limit by changing the spring if not done correctly. Hope this helps you.
ATB