You can calculate the vector-position with c_trace from the camera away (dark-red line) and then angle the gun and the bullet on this target-position.
I made a little image of it:
http://www.haeschen.ch/hopfel/bilder/schiessbeispiel.bmpIf you want I can look for my code I made 3-4 months ago for my 3th person shooter, but it's much better for you, if you elaborate it yourself
