I have an "American Colonial" lock which has broken the half cock notch on the tumbler. It is fitted with a detent and used with a single trigger, so theoretically this should not happen, but nevertheless, stuff happens. I can cycle the lock slowly when it is out of the stock and everything seems to work properly i.e. the sear nose does not catch the edge of the notch. Perhaps the detent hung up some time, but I can't really see any evidence of that (other than the broken notch).
What could I be missing here?