Stop audio looping on Input.GetButtonUp

I'm a sound designer trying to get a basic grounding in Unity implementation so trying to add audio to the Unity 5 Standard Assets Example Project. I'm a code noob so would appreciate any help here.

I am playing a looping sound while the fire button is held down and currently using audiosource.stop to stop the audio playback when the button is released. However what I would like to do, when the button is released, is not instantly stop the sound but play the audio clip through to the end one last time (it's a very short audio clip - 0.3 seconds) and then stop looping.

Here is my code: The sound is on the audiosource in the inspector and I have loop checked in the inspector also.

  var sound : AudioClip;
  
  
  
  function Update () { 
  
    if(Input.GetButton("Fire1"))  
    { 
      if(!GetComponent.<AudioSource>().isPlaying)
      {
        GetComponent.<AudioSource>().PlayOneShot(sound); 
        GetComponent.<AudioSource>().Play(); 
      }
    }
    if(Input.GetButtonUp("Fire1"))
    {
    GetComponent.<AudioSource>().Stop();
  
    } 
  
  }
 

Is the process to uncheck the loop box in the inspector using the code? Will I need to turn loop back on next time I trigger the sound?

The reason I am doing this is that the sound effect stop instantly causing a popping sound as the waveform does not get a chance to return to 0. Is it a possible workaround to trigger a second sound effect on Input.GetButtonUp that is basically a cool down noise - Ie. a premade fadout of the sound?

My thanks in advance for any help on this topic!