The machining in the extractor hole is such that the extractor catches. Just enough though that turning it like Peter suggests will remove it. If it's dropping to half cock, try bending the flat spring (sear spring) towars the sear and it may increase the tension. If you have removed the mag safety, that will sometimes have an effect on the half cock thing. I've seen more than one hammer follow the slide to half cock, and when re-installed, the problem was gone.