There's a pin in the bolt that is easy to lose. It limits the travel of the firing pin. Should it be dry fired without said pin, the firing pin will contact the chamber and leave a nick large enough to stop it from ejecting. If that happens, the nick has to be removed for the gun to cycle. A quick look at the chamber in the area of where the firing pin contacts the rim should tell you if this is a problem.
I would never be so stupid as to do what I described myself, but I've heard of it happening.