Originally Posted by Colorado4Wheel
It could be that his load is so low in pressure that it just doesn't seal the primer at all. I don't know for sure. Perhaps dirty pockets and a low load. To me he has wondered of the reservation with out a guide and anyone is just guessing at this point. I would go back to using the right primer and standard loads and stop fiddling around with non-standard things until he figures it out.
I load plenty low enough for my G17 and never had this problem. I have seen it in other peoples' guns with overloaded rounds though. Kind of makes you wonder, doesn't it?
A "magnum" primer is just a regular primer with a lrch more priming compound. Some "standard" primers are as hot as other magnum primers, and Winchester uses magnum primers for all LP loads.
Heck, many pistol loads are under 10kpsi and they don't pit the breach on guns. 45 Colt for example is well below the OP's pressure and you never see those guys with problems like this.