If you measure the rim thickness of that brass I bet you find it much thinner than standard or SAAMI spec. This will cause the need for double strikes and will allow the primer to raise. You mostly see these when the loads are not hot enough to drive the brass back over the primer when you have excessive headspace. When you fire a round the primer is blown back to the breach, then the brass is forced back over it re-seating the primer flush, that is if the load is hot enough to do this. If you are curious, fire a primed case only and see how high the primer sits over the rear of the case, this is the headspace of your barrel/frame combination. Larry