You've got me thinking now. The front pins on this FT stock must be slightly misaligned. If I take all the pins out I can set the action in the stock bang on centre and square. I can put in all the pins ... 2 front and the 1 at the rear and screw them up so far and it remains all central and square. When I really tighten the front ones the action twists slightly and is then slightly off centre and square. So I have to make sure I line up the scope ret with the action and not the stock.
I think this is going in that other stock to see if this goes away. Shame as I love this FT stock as it makes sure my head is in the same place every shot.