I think in part my issues where done to me doing some maintenance. I have purchased new parts based on advice here however I couldn't change the cylinder\head as the ones I ordered didn't fit. It looks like I had an incorrectly fitted buckling too.
After these changes I was firing at only around 280fps on my chrono (one from AK2m4) who has been really helpful too. I have now changed the spring to an m10 and this now has me around 325 fps on 0.2's I'm popping into my local Airsoft Store tomorrow as I need a new speed loader and will see if they can chrono it too.
Thank you everyone for your advice. It has been really helpful.