Gun archaeologists Max Popenker and Anthony Williams uncovered a previously unknown prototype machine gun that dates back to WWII. Max blogged the below photos, but is tight lipped about the details. The gun will be featured in their upcoming book Sub-Machine Gun.
This gun has some interesting features for a gun of its antiquity. The receiver is stamped steel, the magazine is used as the pistol grip and the bolt extends nearly all the way to the end of the barrel. I look forward to reading about this gun when the book is published.