There are a lot of good posts, here. But what gets me is that your pin backed out and you retightened it. When the pin backed out, it was probably a sign something was wrong. Then the fact that the broken pin got stuck in the case makes me think of an experience I had.
Some european ammo uses a smaller flash hole. IIRC, it's either German or Swiss that use this different standard. I have some with a headstamp DAG. It just backs the pin out when I try to decap this brass. I enlarged the flash holes with a drill, cuz the brass is really good. But if you tightened the pin enough to punch through this hole, I can see it eventually breaking.
Some european ammo uses a smaller flash hole. IIRC, it's either German or Swiss that use this different standard. I have some with a headstamp DAG. It just backs the pin out when I try to decap this brass. I enlarged the flash holes with a drill, cuz the brass is really good. But if you tightened the pin enough to punch through this hole, I can see it eventually breaking.