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It was offcilally adopted by the Italian Carabinieri in 1973, Italian State Police in 1975, Frontier&Custom Guard in 1977, Italian Air Force in 1983 and Italian Army only in 1992 (to replace the previous Franchi LF57 purchased but never issued to the troops).
The Model 12 was the end result of a series of earlier submachine gun prototypes designed by Dominco Salza of Beretta, beginning with the Model 6 in 1954. In 1957, the Model 10 was developed and it was selected as the best design. Further work on the Model 10 resulted in the final Model 12 in 1958. Full production commenced in 1959.
The Model 12 was formally adopted by the Italian Army in 1961 and many other international buyers soon followed. It has been produced under license in several countries and remains in military and law enforcement service to this day.
The Model 12 weighs 3.48 kilograms empty (about 3.820 kg loaded) and is 660 millimeters in length with stock extended (418 mm when retracted). Its short length is achieved by use of a barrel recessed into the bolt head, known as a telescoping bolt. This reduces length without reducing barrel length or bolt weight. It fires from an open bolt and has a cyclic rate of fire of 550 rounds per minute. Its muzzle velocity is 380 meters per second. It is accurate to 200/300 meters.
The barrel and rifling are chromium-plated to prevent fouling. The bolt housing has grooves to allow bolt movement, even in extremely adverse conditions such as exposure to mud, dust, or sand. The exterior surfaces of the firearm are finished with epoxy resin coating for protection against corrosion and damage.
The M12 is a select-fire weapon, allowing a choice of semi-automatic or fully automatic fire.
The weapon has three safeties: a manual safety which blocks the trigger; an automatic safety on the rear grip which immobilizes the trigger and blocks the bolt in a closed position; and a safety on the charging handle, locking the bolt in case it does not retract sufficiently.
The weapon is provided with a front sight (adjustable for elevation and windage) and a rear sight with a two-position flip aperture (up to 100 m and up to 200 m).
The gun is equipped with a side folding stock, but is also seen rarely with a fixed stock.
Twenty, 32, and 40-round box magazines were available for the original Model 12, which was chambered for the 9mm Parabellum cartridge.
The Model 12 was redesigned as the Beretta Model 12S in 1978 and was styled as "the Ultimate Submachine Gun" when released. The Model 12s uses a 32-round box magazine, and is chambered for the 9x19mm NATO cartridge. It utilizes the blowback principle, and is capable of either semi- or full-automatic fire.
A novel feature is the grip safety, which locks the trigger and the bolt in the closed position, thus safeguarding against accidental firing if the grip is not held firmly or if the gun is dropped. The safety and selector switch, which in the original Model 12 were two separate push-pin button (with the selector being a button that activated single-fire or burst fire whether it was pushed on the right side or the left side) have been re-engineered in a modern lever-type selector with three positions (S for "Sicura" or Safety, 1 for semi-auto fire, R for "Raffica" or Burst fire). The fixed firing pin on the face of the bolt can strike the primer only when the cartridge is chambered fully, and this also avoids accidental firing, according to its designers.
The PM12S was also designed with easy field-stripping and reassembly in mind, which has been simplified and can be accomplished without tools. It can be equipped with a suppressor, but this requires a slight modification of the barrel by a competent gunsmith.
Minus the suppressor and other optional features, the Beretta PM12S is made up of 84 discrete components.
The current version of the Beretta Model 12, called the PM12-S2, spawned from the adoption of the PM12S by the French Gendarmerie Nationale, to be assembled under license at the MAS armaments factory in Saint-Etienne from Italian-made parts.[Citation Needed]
The current version of the Beretta Model 12, called the PM12-S2 came from a modification asked by the Italian Carabineri after an 1984 accident, in Rome, were an NCO was killed due accidental discharge.[Citation Needed]
The Gendarmerie/Carabineri asked for a modification, in the form of a further safety device, which allowed both to keep the bolt of the weapon in half-cocked position and acted as an interceptor preventing accidental fire should the bolt or the firing pin suddenly disengage. The so-modified Model 12s were known in French service as the PM12-SD with SD standing for Demi-arme, or Half-cock. In the mid-1990s, this modification was implemented in all the Model 12 sub-machineguns manufactured by Beretta as a standard factory feature, and the denomination of the sub-machine gun changed to PM12-S2; this is the only Model 12 variant currently manufactured by Beretta.