RH, it could be something as simple as the primers seated too deeply on the Polywads. I was shooting some preserve quail last week with an Ithaca Classic Doubles 20ga. That gun has never misfired on me, and I've shot it quite a bit. No problems with various brands of factory shells (including Polywad--although I have not shot that many of them--and RST), nor with reloads. Well, during the course of the morning, I had 4 misfires with factory Remington Gun Club shells. Had used them in the past with no issues. Primers dented, but maybe too lightly. Switched to Estates in the afternoon, fired almost a whole box, every one went "bang". (Also had a couple left-over Gun Clubs, and they both went bang as well.) Sometimes stuff happens.
