At the very beginning of the 70s of the last century, Klimovsky TsNIITochMash received an order from the Ministry of Defense to create a pistol capable of firing without a lot of noise. The basis of the new design was to be a Stechkin automatic pistol. The work on the modernization of the APS was entrusted to the senior researcher of the institute, candidate of technical sciences A. S. Disagreeable. Initially, the project had the AO-44 index. After some minor modifications to the design of the original weapon and the introduction of a silent firing device to it, in 1972 the pistol was adopted as the APB (silent automatic pistol) or 6P13.
The pistol itself has hardly undergone any special changes. The innovations concern only the integral expansion chamber in the shutter casing. To reduce the initial velocity of the bullet, part of the powder gases when fired is vented from the barrel into the tubular expansion chamber put on the barrel through two groups of holes (next to the chamber and at the muzzle). On the front of the expansion chamber, protruding from under the casing, a thread is made for attaching a silent firing device to the pistol. APB automation, like that of the prototype, works on the principle of a free shutter.
A double-action firing mechanism with an open hammer allows you to fire both with manual pre-cocking and self-cocking. In the rear of the breech casing there is a non-automatic fuse that blocks the striker and the breech itself.
The inertial retarder of the rate of fire, as well as the magazine for 20 rounds of 9x18 mm PM, has not undergone any changes. After the appearance of the modernized PMM cartridge, the Central Research Institute of Tochmash carried out relevant studies and came to the conclusion that the APB pistol could not be used with the PMM. The fact is that due to the greater momentum of the new cartridge, the bolt part of the pistol moves too quickly. The consequence of this may be damage to the structure, up to the destruction of some parts.
The silent firing device (length 230 mm and diameter 30 mm) is attached to the pistol on a thread. Inside the muffler casing there is a single structure consisting of a pistol barrel attachment unit and four baffles with holes. All elements of the insides of the silent firing device are fastened to each other with longitudinal bars. During the shot, most of the powder gases remain inside the muffler - in the expansion chambers, after which, after cooling and releasing the pressure, they leave the muzzle. Due to the design features of the sighting devices of the APS pistol, the muffler is asymmetrical - the entrance for the barrel, the holes in the baffles and the muzzle are shifted to the upper side of the PBS. The use of our own barrel of a pistol with holes and a silent firing device did not allow to completely remove the sound of a shot, as, for example, on a PSS pistol. Nevertheless, the noise was significantly reduced to the corresponding indicators of small-caliber weapons. At pistol ranges, this does not completely hide the shooter, but makes it difficult to find him.
The silent firing device, due to the design features, turned out to be not very light - about 400 grams. For this reason, Neugodov decided to abandon the standard wooden butt holster, which was relied on according to the state for the Stechkin pistol. To save weight and convenience for the shooter, it has been replaced with a simple wire stock that is compatible with the old bindings. Interestingly, there are parts on the butt for attaching the muffler to them during transportation. When the buttstock is attached, automatic fire can be fired with great efficiency, using a muffler as a forend. However, during firing, the PBS heats up, which makes it difficult to use it. In addition, the accuracy and accuracy of the APB is slightly better than that of the APS due to a slightly lower initial bullet velocity. Since the old butt holster was removed from the delivery of the pistol, a regular leather holster was introduced instead. The muffler and the stock, respectively, are carried separately from the pistol in the pouch.
From the very beginning of production, APB pistols are manufactured in small batches from the original Stechkin pistols. So, for example, the first copies were converted from the APS of the 50s of release. The main customers of this weapon are the special forces of the Ministry of Defense and the Ministry of Internal Affairs. 40 years after its appearance, this pistol is actively used in appropriate situations, and it is not yet threatened with decommissioning.
