Mr. Vicknair,
Thank you for your prompt and detailed response. You have mentioned many factors, a few of which are new to me, that may be cause for concern. You also stated that the primer failure of interest is not uncommon, but did not mention how common are the injuries involved. You also did not provide any hard statistics of the failures of interest.
So, I spent some hours with Google, searching the subject matter of interest and was rewarded with several reports, discussions, and examples of shotgun primers being pierced or otherwise failing. Not surprisingly, most of these occurred in clays competition and practice where shooters fire many thousands of rounds per year. Somewhat surprising to me was that a major American ammo manufacturer was involved and the persons discussing the issues even knew the exact primer make and model used in the different brand and product shells. One brand label was said to have a failure rate of 10 out of every 25 shell box. The primary gun damage reported was erosion of the firing pins; it was recommended that a qualified gun smith address a correction.
But no injuries to the shooters were discussed. So those shotguns may be of different design from the ones of concern or interest. So, I plan to keep shooting my Parker shotguns, use quality ammo, and be aware of the condition of fired shells and the firing pin condition.

So far, I have not found any source of the hard statistical data of interest, but will remain on the lookout for same. Also, please understand that I m not saying that I do not believe you or that such things do not happen. It just does not seem to me that failures that damage the gun or the shooter are inevitable. Or that it is impossible to make such a gun that does not catastrophically fail.

Best Regards and please do keep me in mind if you do run across an article or report that you find convincing enough to pass on. I will do the same.