Years ago I had a small Sterling .22 auto where the firing pin groove in the slide was large enough that if dropped upside down, the firing pin could slip off the sear from inertia and strike the cartridge.
I experimented considerably with this gun after some "incidents" which indicated a problem. E.g, double taps and a full mag dump where 5 bullets went way, way high in the air and came down I know not where, but there were no "I kooda bin kilt" reports in the newspapers.
I'm not sure, but I think I sawed that gun in half and discarded it. In any case, it's gone, gone, gone.
This was the model (not the actual gun I had)