Cheers guys, I'll scratch that idea from the list. Back to the drawing board
My rationale was that something must be affecting the scope / barrel relationship to induce a POI shift, but as Adam has suggested, there's probably a lot more going on besides.
Since the weather has warmed up, my clubmate's 97 hasn't shifted so he's convinced it's temperature related. I haven't shot enough recently to say either way, but shot my PB last August before the wheels came off over the winter.
Mark, I take it your TX hasn't shifted over a wide range of temperatures etc?
We could do with building a matrix of everyone's setup - rifle, tuning kit, scope, mounts, pellets etc. and when POI shift occurs. That way it would be easier to drill into the detail and highlight any patterns.