The OTs-33 Pernach (ОЦ-33 Пернач, Russian for "multivaned mace, pernach") is a Russian 9x18 Makarov machine pistol.
The OTs-33 is a selective fire blowback-operated weapon firing the 9×18mm Makarov pistol cartridge; it can use both types of 9x18mm ammunition, the standard 57-N-181S and the more powerful 57-N-181SM round. The blowback operation incorporates a feature that separates the slide and barrel as they move to the rear during recoil; there is no positive lock between the slide and barrel as in other conventional designs. As the slide and barrel separate, the spent case is ejected and the slide is then forced back to the barrel by a spring action, chambering a fresh cartridge in the process. The barrel and slide continue to the rear together in recoil for another 5 mm (0.2 in) before returning to the forward position. This feature improves the automatic fire accuracy, reduces felt recoil, and is responsible for slowing down the cyclic rate of fire, without using a sophisticated rate reducer mechanism such as the one employed in the APS pistol. This method of operation also allows the use of standard and higher power 9x18mm ammunition without using a locked breech action. To further reduce felt recoil and compensate for muzzle rise during firing, some propellant gases are diverted into a ported slide cavity that acts as a muzzle brake and compensator, deflecting the gases upward to stabilize the barrel.
The OTs-33 has a double-action trigger mechanism and is hammer fired, with an exposed hammer. The safety/fire selection catch is provided on each side of the pistol at the rear of the slide and has three positions: "safe" (top setting with a single white dot), semi-automatic fire (intermediate position marked with a single red dot) and fully automatic fire (lower setting with three red dots). When switched to "safe" mode, the selector mechanism safely depresses the hammer before returning to the safe position. An ambidextrous lever, which also serves in disassembly/stripping of the weapon, is provided inside of the trigger guard and just in front of the trigger. The Pernach also features a loaded chamber indicator.