I have a Nick Murphy that has been fettled by John Ostler in my AR5s. Found out he actually built my rifle when working at Ripley when I dropped it to him.
Was done about 2 years ago, changed all the o-rings to a wider temperature range set so its more consistant over the year. In fact I have never touched it since John set it to 770fps with JSB Exact. Been within +/-10fps of that over any of the BFTA Chronos at GP's.
Now if I could just get enough time to practise some more then I will be happy.