Thanks to Seggy and Darren
You were both helpful in that the barrel was greasy, and the readings were after the reg.
The gun is now between 565 FPS and 575 FPS over 175 shots.
It is an dream <img src="http://jsramsbottom.co.uk/bbs/e/icon_smile.gif" alt="Smile" width="15" height="15"><!--graemlin:-->