Old & Slow, I feel your pain!
unclenick sure knows his stuff. Overpressure can change dimension of primer pocket. But you say that it is happening on all loads, even low pressure? Now assuming that you are getting blow by on once fired LC or the like, on your low pressure loads, it is not likely that the cases have been overstress by pressure. I find it more likely that your primer pockets were reamed too aggressively and cause a loose enough fit that it did not act as a gas check. I recommend swaging your primer pockets instead to remove the crimp. I also prepare my 5.56 brass with stainless steel pins. It makes for a genuinely clean case. I have found on occasion that two SS pins can get stuck side by side in the primer pocket....so inspect, inspect, inspect.