Armament Research Services (ARES) is a specialist technical intelligence consultancy, offering expertise and analysis to a range of government and non-government entities in the arms and munitions field. For detailed photos of the guns in this video, don't miss the ARES companion blog post:
The Korsac EM-1 (not to be confused with the Thorpe EM-1, which is a completely different rifle) was a bullpup light machine gun based on captured examples of the German FG-42 patatroop rifle. It was developed between 1945 and 1947 by a team led by Polish refugee designer named Korsac.
It was chambered for the 8mm Mauser cartridge, and used an 18 round magazine adapted from the ZB-26. The operating mechanism was closely copied form the FG-42, as were many elements of the rifle's controls, including the capability for firing from an open bolt in fully automatic and from a closed bolt in semiautomatic. Unlike the FG-42, it used a short stroke tappet type gas piston, and had a detachable barrel. Ultimately only two examples were built, and only one of those (the one in this video) was completed to firing condition. It suffered from reliability problems in semiautomatic mode, and was quickly sidelined in favor of the other development projects ongoing by 1947. However, many lessons from its development would be put into the EM-2 rifle.