OK so after a year and adding @mubhaur plenum piece and eliminating 1st regulator my .22cal 600mm m3 was a dream 21grn H+N at 900fps lazer out to 100yrds this continued for thousands of rnds then I started having accuracy issues and when chronied velocity had dropped to 860fps retuned to 900 which held for a couple of tests and went shooting same thing each retune I'm moveing valve adjuster further out then it happens again replaced valve adjuster rod and loctighted end C52 part tuned great went shooting problem back checked C52 right at 6mm...HELP I'm at the end of my rope with this gun!!!!!