Specifications                OTs-01              OTs-01S Caliber, mm................................................9.....................................9 Cartridge.................................9 x 18 mm PM.........9 x 17K (9 mm Short) Overall dimensions, mm...........200 x 130 x 40.................200 x 130 x 40 Empty weight, kg................................ 0.815.................................0.8 Firing mechanism...............................................double action Cylinder capacity, rds..................................6....................................6

    In 1991 the Tula-based Sporting and Hunting Guns Central Research and Design Bureau (TsKIB SOO) received specification requirements from the Russian Ministry of Interior for developing a revolver chambered for the standard 9x18 PM pistol cartridge. The research and development project codenamed Kobalt was fulfilled by renowned designer I.Ya. Stechkin together B.V. Avramov in 1992, The revolver was designated OTs-01 (acronym 'OTs-OI' stands for 'Obrazets TsKIB Pervy' (TsKIB model one)) and TKB-0216, After it had been improved, it received the designation RSA (Revolver Stechkin-Avramov). The first two batches of 100 revolvers each were manufactured directly at TsKIB SOO in 1993-1994. The final version of the revolver was presented in 1995, The RSA revolver was put into production at the Zlatoust Engineering Plant, and the Uralsk Mechanical Plant in Kazakhstan, which received the entire production documentation from TsKIB SOO. in fact, the RSA became the first combat revolver to be launched into series production in Russia after the Nagant revolver had been withdrawn from production.
    The revolver features a traditional design with a closed frame and a swing-out cylinder, swinging to the left. The barrel is fitted with a bar, as well as a streamlined lug for the extractor pin, TsKIB models featured polygonal bore rifling, but mass-produced revolvers had right-hand rectangular grooves, maintaining the traditional technology.
    The cylinder is loaded using a spring-steel clip of a unique shape. Spent cases are extracted by depressing the extractor head. The loaded clip weighs 65 grams. The correct cylinder position in the frame is ensured by the cylinder lifter (latch). Unlike that of other revolvers, the RSA lifter in the form of a rocking lever is mounted in the upper part of the frame, i.e. considerably closer to the chamber. The location of the lifter became probably the main feature of the Stechkin-Avramov design. A reduced arm length between the lifter's center of thrust and the axis of the chamber significantly decreases the cylinder slackness, ensures better alignment of the chamber and the bore and reduces the load on the trigger assembly.
    The revolver is fitted with the external-hammer trigger assembly with a wound-wire cylindrical spiral hammer spring, located inside the grip. The trigger assembly enables the revolver to conduct double-action and single-action fire. There is a hammer stop, and the hammer is blocked from moving forward after a shot is fired When the pistol is fired, the hammer hits the inertial striker (firing pin) mounted in the frame. If the cylinder does not rotate all the way, the hammer block does not allow the hammer to hit the striker. The trigger assembly activates a vertical sliding bar, which presses the cylinder lifter (flock) downwards. The same sliding bar acts as an automatic safely, which protects the rear end of the striker and prevents the hammer from hitting it until the trigger is fully pulled Symmetrical grooved plastic grip plates are screwed to the frame and wrap it all around so that the firing hand does not touch the frame metal. Shooters with small palms may use revolvers with a rounded grip, while those with large hands can be provided with a flared grip. The first batch of revolvers, manufactured by TsKIB, was equipped with wooden grip plates. The shape and the grooves of the trigger guard are designed for two-handed firing. There is a ring in the base of the grip for attaching a safety cord or strap.
    A rectangular-groove rear sight is fixed in the lateral notch of the frame and features thick edges for protection against damage. A foresight is pinned to a low base. Its front edge is rounded for convenient carry in a holster, while its rear edge is slanted to rule out glare. The upper surface of the barrel and the frame rib are covered with fine grooves with the same end in view. The location of the iron sights ensures a relatively long sight radius. The bullet dispersion at a range of 25 m is 10 cm. The foresight and the rear sight are fitted with white plastic inserts for aimed low-light firing.
    There existed also a prototype revolver with a shortened barrel, and more powerful models chambered for the 9x18 PMM high-power cartridge and 9x19 Luger round. However, these versions did not arouse much interest.
    A so-called «service» revolver, designated TKB-0216S and chambered for the 9x17 short round, was developed for private security personnel and private detectives. The TKB-0216T model, manufactured by the Zlatoust Engineering Plant and chambered for the 9 mm RA cartridge with a rubber bullet, is a civilian non-lethal model.
    After TsKIB SOO had joined KBP, the latter became the main provider of RSA revolvers.