The Vz61 “Skorpion” was a machine pistol developed by Czech engineer Miroslav Rybář in 1959. It was actually his thesis project for his post-graduate studies at the Czech Military Technical Academy. After some minor revisions it was formally adopted by the Czech military in 1961. In fact, the lack of major revisions needed between prototype and production of the Skorpion are an impressive tribute to Rybář’s abilities.
Mechanically, the Skorpion is a closed bolt, blowback operated firearm. It feeds from 10- and 20-round magazines mounted in front of the trigger guard. The original caliber was .32 ACP (aka 7.65mm Browning), which was a standard handgun caliber in Czechoslovakia at the time of its development. One unique feature is the use of a rate-reducing plunger/weight located in the grip. The bolt locks open temporarily at its rearmost point of travel, and is only unlocked when a plunger has traveled down a tube inside the grip and then been pushed back up be a spring. This mechanism reduces the cyclic rate to 800-850 RPM, which is much more practical than what a typical blowback .32 caliber SMG would produce.
The Skorpion has a selector switch on the left side of the receiver to change between safe, semiauto and full auto firing modes. It also has a folding wire stock to allow a shooter to fire from the shoulder. In military testing, it was found capable of putting 20 rounds into an 8.66 inch circle at 100 meters.
The original Vz61 was chambered for .32 ACP, and approximately 210,000 mere manufactured between 1961 and 1979. In addition to Czech use, it was adopted by Yugoslavia, which purchased 30,000 and then licensed the rights to manufacture them (under the designation M84).
The Vz64 was developed for the 9×17 Browning cartridge, also known as .380 ACP. It added compensator cuts to the barrel and used straight box magazines (the .32 models had curved mags). No changes to the mechanism were necessary.
The Vz65 was externally identical to the Vz64 except for the compensator cuts, and chambered for the Soviet 9×18 Makarov cartridge. This change did require modifying the rate reducer to tolerate the greater bolt velocity generated.
The Vz68 was developed as an export variant in 9x19mm Parabellum. This caliber is much more powerful than the .32 ACP, and significant modifications to the mechanism were necessary. The bolt weight was doubled, requiring an increase in the size of the upper and lower receivers. A rear sight leaf calibrated for 250m was added, as well as sling swivels and a matching variant with a fixed wooden stock.
The Vz82 was chambered for 9mm Makarov like the Vz65, but introduced a number of manufacturing changes. Most notable was the use of a stamped and welded lower receiver in place of the milled component used on all previous versions. It also added a telescoping element to the stock, simplified the trigger mechanism, and replaced the two cocking knobs with s single one that could be mounted on either side of the bolt.
Several commercial variants are still manufactured by the CZ factory, in several calibers and in both semiauto and select-fire configurations:
There is a weighted block in the pistol grip which is pushed upwards by a spring. When the bolt cycles fully rearward, it hits a cam that pushes the weight down, and simultaneously engages a hook that holds the bolt at its rearmost position. The weight in the grip takes a shot period of time to travel down, stop, and then be pushed back up by its spring. When the weight returns to the top of the grip, it causes the bolt hook to disengage, allowing the bolt to return to battery and load a new cartridge. By adjusting the mass of the grip weight and the strength of its spring, the rate of fire can be fine tuned to whatever the factory prefers – in this case, 850-900 rounds/minute.
Cutaway vz.61 parts and mechanism diagram:
A Vz61 made for Yugoslavia, plus a couple extra photos (download gallery at high resolution):
Additional photos of a cutaway vz.61, courtesy of reader Denny: