Without seeing the rifle, I can only make a few guesses. Is the magazine and trigger guard vertical in relation to the stock? If not you might need to sand a tiny bit around the lugs to level. Does the action and barrel rest evenly in the stock with the bolts loose or out? If so, how tight are the bolts before the action and barrel drift? Could the bolts be over tightened? Is the wood the same thickness on each side of the stock?