Ah cheers..Raj. Stripped it down and vernier calipered the cylinder and it was spot on parallel .reassembled the filling valve with new rings . Cocked the rifle S510 BTW and it took a fill up to 190 bar ..very odd but think I just let too much air in too quicky .Apparently they are tested to 250 bar...

I just got my cylinder back from being hydrostatic tested and refilled (300 bar).only needed a small top up but the knob was stiff and when it did open it shot up to 230 and something went ping ....then the filling loop depressurising just leaked ..in panic I removed the quick release (brass )female...