Expat is correct that a long case neck could create a pressure problem though it appears that the overpressure is pretty extreme and excess powder is still the most likely culprit.
One other suggestion is that you reduce your picture sizes. When you post the huge pics the screen can't contain it all and the posting has to be scrolled back and forth on a lot of our computers. If you crop them down to size that will help and not reduce the clarity.
Frank
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