FNA (Fabbrica Nazionale d’Armi) Brescia was a factory in the Val Trompia in northern Italy, the same valley that is home to Beretta and many other, smaller Italian arms shops. During World War Two the factory mad a lot of small arms for the Italian military, including some interested designs like the FNA-B 43. After the war times were hard for the company, though, and the X4 and X5 are pretty much their last project, from the 1950s. This was a very simple, inexpensive stamped submachine gun / machine pistol system. There was nothing particularly wrong or bad about the guns, but also nothing particular exceptional about them. Shopping some samples around the market led to no contracts, and they never went into full production.
Thanks to Beretta for giving me access to this example from there reference museum to show to film for you!
Full video on the FNA-B 43:
