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 weapon has a selective fire option allowing a choice of single shot 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 cocking 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. The Model 12s uses a 32-round box magazine, and is chambered for the 9x19 mm NATO cartridge.
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 fire-selector switch, which in the original Model 12 were two separate push-pin button (with the fire-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 Single-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.
Cartridge: 9x19mm Parabellum
Rate of fire: 550 rounds/min
Muzzle velocity: 380 m/s (1,247 ft/s)
Effective range: 100 to 200 m sight adjustments
Feed system 20, 32, 40 round detachable box magazine
-M12: 3.0 kg (6.61 lb)
-M12s: 3.2 kg (7.1 lb)
-M12s2: 3.480 kg (7.67 lb)
-M12: 3.4 kg (7.5 lb)
-M12s: 3.6 kg (7.9 lb)
Fixed stock: 660 mm (26.0 in)
-645 mm (25.4 in) stock extended
-418 mm (16.5 in) stock folded
Barrel length: 200 mm (7.9 in)
Height: 180 mm (7.1 in)
-Two-position flip rear aperture
-shrouded front post
-285 mm (11.2 in) sight radius