I added the red circle to highlight the bolt release of an AR-10. See "source" for a link to the original image.
Vitaly V. Kuzmin
CC BY-SA 4.0
<a href="//commons.wikimedia.org/wiki/File:AR-10_National_Match_-_ArmsHunting13-45.jpg" title="File:AR-10 National Match - ArmsHunting13-45.jpg">File:AR-10_National_Match_-_ArmsHunting13-45.jpg</a>