No expert here by any means BUT one other though they comes to me is how you are resting the rifle in what ever rest you are using when shooting. If you place that rifle in the rest more towards the rear and then on a couple shots the rest is more towards the front of the forearm where you say it is most flexible then you could be putting upward pressure on the barrel causing the fliers. I would make sure that with that stock that you support it as far back as you can to eliminate that variable.
