The clandestine 8mm and 9mm were products of Canadaicon which were supplied to the US Gov't.

I understand that the "9 MM 4x" headstamped ammo was the standard US Gov't issued 9mm until the adoption of the Beretta M9 pistol.

International Ammunition Association {iaaforum.org} - View topic - Canadian 7.9 addendum

International Ammunition Association {iaaforum.org} - View topic - Canadian 7.92MM and 9MM Hdstmps.

International Ammunition Association {iaaforum.org} - View topic - 7.92x57 refresher