Suomi KP/-31 Compilation in Movies

The Suomi KP/-31 (aka Suomi M/31), commonly known as the Suomi submachine gun (Suomi konepistooli) in Finland, was a sub-machine gun based on the early Bergmann MP18 design. First designed in 1922, by Aimo J. Lahti, the gun was revealed to the public in 1925. The Suomi (Finnish for Finland) KP/-31 was in service in the Finnish Armed Forces from 1931 to the 1960's, and was also deployed in large numbers by other military forces during the Second World War. Some special versions stayed in service through the 1980s.

A semi-automatic model was introduced in 2009 by the TNW Company of Verona, Oregon. The TNW M31 has a few distinctions. First off, in order to pass as semi-automatic only firearm and not a converted automatic, the TNW receivers are smaller internally than the original, which prevents the fitments of a fully-automatic bolt assembly. Next, the appropriately undersized bolt is fitted with a hammer-fired firing pin, as opposed to the original’s fixed firing pin. Some early models of TNW’s M31 featured a striker fired bolt assembly, but the design was changed over to a hammer fired setup for reliability. The TNW M31 fires from a closed bolt, rather than an open bolt as on the original KP/-31. The barrel was lengthened to 18.75″ in order to meet both US and Canadian legal standards.

While somewhat similar in appearance and shape to the Soviet PPD-40 and PPSh-41, the KP/-31 is not functionally related to the two. However, Soviet experiences against the KP/-31's 71-round drum magazine during the Winter War did inspire the drum mags that would later be used on their own PPD-40s and PPSh-41s; this is the only significant relation between the designs.