When you shoot, how do you detect whether you hit?
I'd suggest performing the same kind of check (would guess some ray cast) and just use that.
If going that route, you could also cache the result, so you don't have to do another check when firing, but that might depend on your weapon (e.g. if you have a weapon with a high amount of spread, your crosshair might be red, even though bullets might miss).
got the previous crash without ~Ausfaelle(); but with that I get undefined symbol and no crash. My app doesn't even load. undefined symbol: _ZN9AusfaelleD1Ev
~Ausfaelle(); is the declaration of a class destructor.
If you've declared it, you also need to define it (in the .cpp, like you do with the other normal class functions).
I would also suggest you use a debugger and step through, and see where the application crashes.
EDIT: That said, I don't see your class as needing a custom destructor. If you do not provide one, a default destructor is generated for you. You need a custom destructor in certain cases*, but I don't think your case requires one. I think something else is going on. Stepping through with a debugger seems like the best bet.