Are you sure about that?<p>The lower receiver - the part of the gun that&#x27;s a controlled &quot;firearm&quot; - is identical between the AR-15<i>, M-16, and M-4. The only things that really change are the barrel length and the parts that go in the lower to differentiate between automatic fire and burst fire.<p></i> the &quot;real&quot; AR-15, by Armalite - not the semi-automatic version commonly available to civilians.