So I picked up an AR15 upper on the EE, which arrived today. Went to clean and relube the BCG, and the FPRP wouldn't budge. Took a look from the back of the BCG and this is what I saw:
Tried rotating it 90 degrees to get it unstuck from the firing pin. It backed out about 2mm:
First of all, how does this even happen? Second, how can I remove it without damaging the BC?

Tried rotating it 90 degrees to get it unstuck from the firing pin. It backed out about 2mm:

First of all, how does this even happen? Second, how can I remove it without damaging the BC?