title: How to make unity transform axis look at specific direction
body: <p>I have a hierarchy like this:</p>
  
  <pre><code> --gun
    \--bullet
  </code></pre>
  
  <p>In unity3d and I want the bullets specific axis meet with the guns specific axis</p>
  
  <p>like this:</p>
  
  <p><a href="https://i.stack.imgur.com/EaTH7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EaTH7.png" alt="enter image description here"></a></p>
  
  <p>Note the Bule(<code>z axis</code>)</p>
  
  <p>And here is the gun's transform</p>
  
  <p><a href="https://i.stack.imgur.com/PbzE0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PbzE0.png" alt="enter image description here"></a></p>
  
  <p>And I want to rotate the ball's transform so that the Z axis of the ball  coincides with the guns Y axis</p>
  
  <p>like this:</p>
  
  <p><a href="https://i.stack.imgur.com/oDpKv.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oDpKv.png" alt="enter image description here"></a></p>
  
  <p>So How could I do that? thanks</p>