I've been asked:

[suum cuique]

Somebody with a Luger asked :
If he manually loads the weapon, (pulls the toggle) and then pulls the trigger, his gun fires and reloads the next round in the chamber. If he pulls the trigger again, the gun will not fire.
If he reloads again manually by pulling the toggle, then the gun fires but the next round will not fire again.
What could cause his problem?

I 've thought maybe somebody here has a clue. I thought it could be the trigger, but I have not seen this gun.
I don't know what kind of luger it is.