Finland’s armaments industry quietly produced one of the very best submachine guns of the Second World War. This weapon was the KP/-31 (also known as the Suomi m/1931). The design is not well-known now, but in its day it was the weapon that everyone else wanted.
As can be seen from the videos in this article, the gun’s design and basic layout were not revolutionary. What separated it from its peers was the fact that it was extremely well-made. No expense was spared in its manufacture: the components were machined to a high degree of refinement, the magazines fitted solidly into the feeding mechanism, and the weapon could withstand all kinds of extremes of cold and dirt.
This last point–the feeding mechanism–was liked so much by the Soviets (who found themselves on the receiving end of the KP/-31 during the Winter War of 1940) that they incorporated this design feature into their own knock-off copy, the PPSh-41. The Soviet military valued toughness and reliability in its weapons, and it was rare for it to adopt a foreign design so completely. The fact that it did so is a testament to the KP/-31’s quality. The weapon was fitted to use either a 50 round box magazine or a 71 round drum. The box magazine used an odd feature where the rounds were fed through two “columns” in the magazine. In practice, this did not present any problem.
The weapon proved itself in combat and was quickly appropriated by any nation that could get its hands on them: Sweden, Denmark, Switzerland, and Poland, to name a few. Even Germany valued the weapon and purchased a few thousand models for its own operations. Examples were found in use all over the world, even with Communist forces in Korea during the conflict there (1950-1953).
By all accounts the weapon handled superbly, was a joy to fire, and was resilient to a degree that none of its competitors could equal. At a time when many militaries were churning out mass-produced weapons held together with cheap pins and metal stampings, nearly every piece of the Suomi m/1931 was machined out of solid metal. This, of course, made it impervious to breakage and wear. It was apparently accurate up to distances of about 350 yards, a fact which made it nearly an “assault rifle” in practice.
Length (overall): 34.25 in.
Weight (with loaded drum magazine): 15.52 lb.
Rate of fire: 900 rpm
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