Above: A M4A1 with SOPMOD package, including Rail Interface System and Trijicon 4x ACOG. The barrel length is 14.5 inches.<br>Below: A M4A1 with a Close Quarter Battle Receiver. The barrel length is 10.3 inches.
<a rel="nofollow" class="external text" href="http://www.dtic.mil/ndia/2003smallarms/john.ppt">http://www.dtic.mil/ndia/2003smallarms/john.ppt</a>