I don't know why they would use MIM on a pin either. Most likely it is just cut from a rod. I would bet the pin wasn't in all the way and seated properly because I have no idea how you would break a pin like that lol. I do believe this is considered a pretty freak occurrence. I would just pick up a few when you get a chance since this is such a small thing. I would just be glad everything else is working properly. It obviously isn't a mechanical error in the gun itself.