Just saw this thread and my first thought was that it may have been caused by having the rifle set up in a Caldwell Lead Sled that kept it from recoiling back like it should. I've heard a lot of that happening out on the net and it's usually from one of the bigger calibers that has a lot of ft/lbs. of energy. Physics says that when there is an action there is an equal and opposite reaction. I'm wondering if that was a partial cause and the screws not being torqued properly also entered into it because that's the weak area on a stock where it usually happens.