Yep, I'll check the stocks for pressure points.
One thing that especially puzzles me is that it get MUCH worse with short rifles.
Mosin Nagant 91/30 - hits 2'' left at 100
Mosin Nagant m44 - hits 6'' to the left at 100
Both had their front sights still aligned with the factory mark on the sight bases. Used the same ammo in both rifles.