Patent of the 39M
<a href="https://en.wikipedia.org/wiki/P%C3%A1l_Kir%C3%A1ly" class="extiw" title="en:Pál Király">Pál Király</a>
Filing date: Nov 13, 1939; Issue date: May 16, 1944
<span><a rel="nofollow" class="external text" href="https://patents.google.com/patent/US2348790">U.S. Patent 2,348,790</a></span>  <a rel="nofollow" class="external text" href="http://www.google.com/patents/about?id=J25NAAAAEBAJ&amp;dq=2348790">Google</a> <a rel="nofollow" class="external autonumber" href="http://world.guns.ru/smg/smg104-e.htm">[1]</a> <a rel="nofollow" class="external autonumber" href="http://world.guns.ru/smg/39m_pat.jpg">[2]</a>