Hey folks,
I have had similar problems with cob media getting stuck in the flash hole and primer pins getting bent on occasion. I gave up on the idea of simply polishing and then sizing right away. Instead, I found it necessary to carefully inspect each case for stuck media after polishing.
I prefer to carefully inspect my cases and do any trimming or culling before the polishing process, so inspecting after polishing is an unwanted operation. To eliminate this additional inspection process, I polish most of my cases after the reloading process. I know some folks may say this is dangerous, but it simply is not true. I do not tumble my cases. I use a vibratory machine with corn cob media, and the loaded cases simply flow in the media and come out as bright as usual.
No, I have never had any round go off, and I have been doing it since I first bought my Lyman vibratory cleaner nearly twenty years ago. The finished bullets shoot to the same point of impact as non-polished rounds, and I do not buy the idea that the powder breaks down inside the case. It just isn't so.
Now, having said that really crazy idea, I will let others have a go at my suggestion.
Best wishes,
Dave Wile