Had it not been for the German and Russian invasions in 1939, Poland might have entered the 1940s with a very modern semiauto infantry battle rifle - the wz.38M. Designed by Josef Maroszek (notably also the designer of the wz.35 Ur antitank rifle), the wz.38M is a simple and efficient rifle which includes elements from the BAR as well as several Czech firearms.
It is a gas operated action with a Browning/Petter locking system, in which the bolt tilts up and down, locking against a cut in the top of the receiver. It disassembles into 4 components (plus one pin) in moments - really quite impressive for its time - and even still very good by today's standards.
In total, just 55 of the rifles were made as an experimental trials batch, delivered to the Polish Army in 1939. Archival records of the weapon end at that point, as the German and Russian occupation ended Polish arms development. Only 5 examples are known to survive today, with two in Poland, one in Germany, and two in the United States.
Cool Forgotten Weapons merch! http://shop.bbtv.com/collections/forgotten-weapons