Sort of a dumb question for the group:
I know that pierced primers are usually a sign of over pressure. If I rule that out (for example, indirectly with chrono data) and the piercing or flow is just from the soft Federal primer in my 9 mm loads, IS THERE ANYTHING DANGEROUS OR PROBLEMATIC FROM HAVING THE FIRING PIN PIERCE THE PRIMER?
I don't know if there are other
ways of getting a pierced primer, but I do know of two ways:
1) have a damaged firing pin that has a jagged or sharp point (and/or exacerbated by primer swipe)
2) have excess pressure
You said in your post "what if I rule that out?" (over pressure) but I would suggest that without pressure testing equipment, you simply cannot
rule out an over pressure situation.
Dangerous and problematic is that when you have a pierce primer, you've got white-hot gas forcibly trying to escape somewhere other than out the muzzle behind a bullet. That's bad!
No good will come of it.