Hi guys thanks for your advice
Have sent the gun back to aa. Apparently (now i'm not 100% as it was all quite confusing) there is a valve that completly empties the chamber if the pressure falls below 50bar and this was faulty letting the air excape down to 50. Anyhoo aa are fitting all new valves, seals etc and fair play to york guns who have given me a Daystate to tide me over until mine comes back. Seems odd that it has a low pressure release valve but no high pressure release...I guess the answer is dont overfill!
Thanks guys
Geoff