Oil in the breach plug got me once bad too and carbon built up MUCH faster. I popped a couple of primers and then tried some CCI209Ms but still had issues until i gave it a good cleaning.

I seldom use mag primers except in extreme conditions or just for testing. Close to 90% of my shots have been with Win209s or even weaker primers and no hang fires. Most of that credit goes to the Lehigh and Ron's plugs though because the primers fit very well and blowby is nearly zero.