Ballistic advantage bcg firing pin retainer issue.

[battlemidget]

You tried twisting the pin while inserting?
You have another BCG and pin that you can try some mix n match and see where the problem follows?
Can the pin make it through the first hole? If so, spend a minute twisting the tips in the first hole, in and out, etc.
Pliers/file would be my last resort, but I'd file the outside of the tips if I got to that point, and I'd be more comfortable with the filing process if another pin worked fine (almost confirming that it's the pin since another pin worked ok).

EDIT- BAMFG is a good shop, drop them a line about your troubles and they might swing you a nice spares kit.