Colorado:
Regarding over-size firing-pins, the primer is not pierced by the firing-pin, but is likely to blow out into the firing-pin hole, pushing the pin back in the process, and venting into the action and stock-head. In that case the primer ruptures because it is largely unsupported, having already been stretched and weakened by the pin-strike. It is not pierced!

This doesn't happen when firing shotshells in guns with oversize firing-pins as the pressure is relatively low. Chambering a full nitro rifle cartridge is going to increase the pressure by 3 to 8 times, depending on the cartridge! That primer needs to be very well supported indeed! I'm repeating my earlier post I know, apologies, but apparently it's necessary.

In the case of the FN shotgun mentioned earlier, it was a pierced primer due to a damaged firing-pin. I related that account simply to draw attention to the potentially disasterous effects of high-pressure gas getting into the firing-pin holes. Bushed strikers will prevent this happening regardless of the cause.