If the primers are backing out past the head of the case, then it's probably a headspace issue combined with the soft/oversized primer pockets that has allowed the primers to back out that much. If the headspace were correct the primer wouldn't have room to back out that far because the bolt face would be in the way holding it in. What I've noticed from cases if handloaded that had their primers seat a little too easily (a sign that they are at the end of their useful life) is that these primers would flatten out flush with the case head on firing while the cases with identical charges with good pockets wouldn't back out at all. This is why I use a hand priming tool and pay close attention to the amount of pressure needed to seat the primer. If it's a little too light, I mark the case head with an "X" with a black magic marker so that I know to toss that brass after it is fired one last time.

Mike