Ziggy, NOT saying this is what happened to yours, but that stud can be broken if the action of a revolver is fully cycled and dry fired with the sideplate off and without full release of the tension of the hammer spring. That hammer stud is captured in the corresponding blind hole in the sideplate which supports the stud on both ends during normal firing action. I think it's also possible for these studs to come loose where they are captured in the frame as well, but I also think most of the ones that are broken completely off were likely dry fired with the side plate off. You can cycle the action with the hammer spring in place, but you should hold the hammer spur with your thumb and allow the hammer to fall slowly and with that support! I make this post to be informative to all of us, including myself, since many are not aware of this possibility. These posts just brought it to mind for me.

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So long ... Ken