I have an AR with about 1500 rounds through it. The firing pin has become pitted. But the pits are very shallow. Is it time to replace the firing pin? Generally, at what point should a firing pin be replaced?
Thanks.
What brand of FP? Most a hard chromed and usually it’s just carbon build up with can be scratched off with a steel brush.
RRA brand.
from the Maintenance Manual:
Check firing pin 15) for Firing pin is
chips or breaks If damaged, damaged.
evacuate to support maintenance.
and this:
The tip can pit if you get a bunch of pierced primers. But other than that, I don’t see how a firing pin could be pitting. 
I think Gotm4 is right and it may be Carbon build up. I will take a closer look tonight.