Finnish 9mm (long)

[Roadkill]

This has come up before, more info:

There were two main categories of 9 x 19 mm Para cartridges and two manufacturers of them: VPT (State's Cartridge Manufactures; there were at least two loading plants using headstamp: "VPT", one in Lapua, another in Kanavuori, but the cartridge loading activity was de-centralized during our Third Independence War 1941 - 44 very efficiently even to the private homes), and SAKO. Headstamps: "S" or "SO", not "SA".! Sako Oy, a firearms and ammo manufacture of Finnish Civil Guards, Suojeluskunnat, had also two plants, one in Riihim�¤ki, another in Kalkku, close to the city Tampere. Kalkku plant was entirely underground, accommodated into a large cave quarried on the rocky wall. Nowadays it is occupied by Finnish Red Cross as a large store-house.

It is difficult (and to me: it is IMPOSSIBLE) to get complete information about Finnish military ammunitions in general, or even about the 9 x 19 mm cartridges. History of the Finnish ammo production is never written. There was, as mentioned above, two kinds of 9 mm cartridges, namely Pistol loads and Submachine gun loads. Pistol cartridges had usually a bullet weight 7.5 grams and muzzle velocity 340 - 350 meters per second. During the war had all Finnish military cartridges Berdan primers, with one exception: 12.7 x 99 mm aircraft machine gun cartridges (produced by private-owned Tikkakoski Oy) were primed with "8 mm Boxer caps". 9 mm pistol cartridges had a convex bottom of the case head.

9 mm, 8 grams, 400 m/s

The SMG cartridge was developed by the idea of firearms designer Aimo J. Lahti. The case head bottom was concave, somewhat stronger than the head of pistol case. According to the "brainstorm" of Aimo Lahti, the bullet weight should be 8.0 grams and muzzle velocity from the barrel (length 314 mm) should be 400 meters per second. Maximum allowed chamber pressure should not exceed that of 9 x 19 mm pistol load, or 2600 atmospheres (bars). Outside dimensions of SMG cartridges should be similar to those of the pistol cartridges. Since start of Suomi submachine gun production in 1930, the sights of KP/-31 guns were graduated along with ballistics of oval-pointed bullet, weighing 8.0 grams and having the muzzle velocity 400 meters per second.

Photo: Filling Suomi drum with wartime 9 mm pistol rounds.

Idea of SMG cartridge was born presumably in late 1920s, but there were some problems, created by the reduced powder space of strengthened cases. A new kind of powder was needed to allow loading with heavier compressed-load charges without exceeding the maximum limit of chamber pressure. The new propellant was presumably VihtaVuori's N 13 (from 1st September 1973 known as N 330. Still in production, and called - inofficially - as "the submachine gun powder"). I don't know, whether the bullets with a weight 8.0 grams were actually adopted. I have met just those with weight 7.5 grams from the war-time loads. There was a severe shortage of copper and lead in Finland during the war-time in 1939 - 45. Half gram of "strategic materials" per bullet means a ton of them when 2 millions of bullets are produced. A daily consumption during the most ardent phases of wars, when life or extinction of Finnish people was at stake.

A special powder for special loads

The submachine gun was re-considered as a short-range "mowing machine"; no more as a selfloader carbine with the burst fire option and range within 500 meters. Even with the 7.5 grams bullet weight, the SMG cartridges were not recommended to shoot from the pistols, although the chamber pressure generated was within the limits given for normal 9 x 19 mm Parabellum loads. SMG cartridges were loaded with heavy charges of "cool" powder, presumably mixed with potassium carbonate, Glauber salt or other non-oxidating salt in the "powder dough". When the water-soluble salt is washed away from the extruded and cut powder kernels, their surface turns rough or "porous" like a sponge.

More common salts for this purpose are oxidating inorganic nitrates like potassium or barium saltpeters. Non-oxidating salt mixed into the powder "cools down" the burning temperature. Powder gasses contains more carbon monoxide, hydrogen, nitrogen and methane (all light gasses) and less carbon dioxide and water steam (dense gasses), when the hydro-carbon is burned with a shortage of oxygen. Volume of the light powder gas, generated from the cellulose, is more large than the volume of dense gasses, which needs much more high burning temperature to become expanded for production of equal kinetic projectile energy.

This "cool burning" of nitrocellulose powder was discovery of Russian professor Dmitri Mendeleyev (at University of St. Petersburg) in 1890 - 91. Western literature is usually ignorant of "The Mendeleyev's Principle", which is especially useful when adapted for the powder of cartridges in full-automatic firearms with air-cooled barrels. I don't know the actual bullet velocities of Finnish SMG cartridges, but it was presumably 400 + m/s from 314 mm barrel of KP/-31, because the bullet weight was lightened, bullet was shortened and the available volume of powder space was accordingly increased.

Not for frail pistols!

Volume of the powder gas, generated by increased charges of "submachine gun powder" burning by the Mendeleyev's principle developed a long-lasting remaining pressure into the bore of submachine gun, where it was beneficial, but also into the pistol bore, where it might be harmful. Some pistols with a short recoil mechanism are designed to shoot loads generating just a low remaining pressure when the breech-bolt starts it's independent movement backwards after "unbolting". Best known example is Mauser C-96 (photo at right): Remaining pressure blows the breech-block back and completes the reloading cycle. Some other handguns, like Luger/Parabellum P-08 and Lahti L-35 (= in your country, Sweden, Husqvarna Model 1940) needs no remaining pressure at all for functioning of action.

Shooting with SMG cartridges could sometimes wreck Parabellum pistol by first shot, and many L-35 pistols in collections have a fracture on their "Achillean heel", below the fulcrum of accelerator lever, on the left side of receiver, behind the barrel. Pistol L-35 without this fracture has presumably never been "Over There" (= in the actual battle). At least it has been never "discharged in anger". Fourth kind of 9 x 19 mm pistols, issued to Finnish Air Force personnel, was omivorous: Safe to shoot with SMG cartridges. It was Browning Hi-Power or F.N. GP-35 with a refined Browning mechanism of action (light barrel and heavy slide, connected with ribs during the high pressure).

rk