Answers to questions-the gas blow-by is occurring in all brands of cases (RP, LC, PMC, FC) The primer pockets are reamed if they had crimped primers. The primer pockets are all clean- the RP cases were new and the once fired I ran through a SS pin rotary tumbler to clean the cases and primer pockets. I'm seating with either the RCBS Rockchucker single stage press or my Dillon 650 progressive.
I think the next logical step is to try a different brand of primer unless there are any other suggestions.
best wishes- oldandslow