Could be...that your stock bolts are not properly torqued. Bart can probably tell you which one gets tightened first. First thing...you have to make sure the barrel and receiver is properly seated into the stock. I think that you should first --- hold the barrel of the gun with the muzzle vertically straight up --- and tap the butt stock gently on a carpeted floor, to make sure the barrel and receiver is properly seated into the stock. I think you should call a qualified gunsmith, as to which stock bolt gets tightened first.
With my faint recollection....the stock reciever bolt gets tightened first, then the forearm bolt. Go back to the receiver bolt for the final torque --- then the forearm bolt. Could be that that your stock bolts are too long.