So I was out shooting when my AR started acting up. It would fire a round but not eject the spent case, it appeared to be short stroking all of a sudden. I pulled the bolt and installed new gas rings and that didn't solve the problem. Threw a different BCG in the gun and all worked fine. Tried a different bolt in the suspect carrier and all worked fine. Tried the suspect bolt in a known working carrier and back to short stroking.

What else could be the problem with the bolt?