True, a very common event, probably not dangerous. Headspace of any given rifle chambered for a rimmed cartridge, is the distance between the boltface and the rim recess of the barrel abutment. It was originally checked by closing the bolt on a soft lead wafer and measuring the result. But...my opinion only, any cartridge that headspaces on the rim, should not allow primers to back out. And if it does, the excessive headspace can only come from a stretched action frame or worn bolt lockup.
