The ZK-391 is one in a series of Czech developmental semiautomatic rifles designed by Josef Koucký. It was developed initially in 1939 (hence the “39” in the designation), and was tested by the Italian military in 1943. It was ultimately not put into production, but nonetheless is an interesting detail of rifle development – a Czech design made under German occupation (note the Waffenwerke Brunn marking) for Italian trials (note the Italian safety markings).
Mechanically, the rifle shared many elements with the M1 Garand, including the two-lug rotating bolt, the long stroke gas piston, and the removable gas tube. It has several unique elements as well, like the trigger guard doubling as a lever to recock the hammer and the out of battery safety mechanism incorporating the receiver top cover.
Thanks to the Institute of Military Technology for allowing me to have access to this rifle so I can bring it to you!