Probably not an answer to warping, but twice I have seen stocks in bolt action rifles "seem" to warp after shooting. The actual culprit was the screw from the front of the trigger guard into the receiver. That screw was too long to fit the wood so that no matter how much it was tightened the screw could not tighten the receiver to the wood. The results were patterns that wandered from the initial shot.

http://www.bakercollectors.com/