Single shot bullet to full Automatic + Damage calculation

Is there a script for this?

That question is too general. Have you looked at any of the example projects?

Like this one, for example: http://unity3d.com/support/resources/example-projects/3rdpersonshooter (Live demo here: http://unity3d.com/gallery/live-demos/index.html#3rd-person-shooter)

Or this one: http://unity3d.com/support/resources/tutorials/fpstutorial