The KS-23 was designed in the 1970s for suppressing prison riots. It was created by TsNII-Tochmash, a key Russian weapons developer, for the Russian Ministry of Internal Affairs (MVD). The barrel for the KS-23 was made from 23 mm anti-aircraft gun barrels that were rejected due to manufacturing flaws. These rejected barrels were deemed to be acceptable for the lower stress of firing slugs and less-lethal rounds, and thus were cut down in length for use as shotgun barrels. The KS-23 began to see use during the mid-1980s by several MVD forces. During the 1990s, research was made into improving the original design to make it usable in confined indoor areas. Two prototypes were proposed, the KS-23M and KS-23K, although only the M version saw use. Today, both the standard KS-23 and the KS-23M are in use by Russian law enforcement.
The original KS-23 was developed jointly by NIISpetstekhniki (MVD) and TsNIITochmash in 1971, it was accepted for use by the Soviet police in 1985. The gun has a barrel length of 510 mm and an overall length of 1040 mm. The KS-23 has an underbarrel tubular magazine capable of holding three rounds, with one in the chamber giving the gun a maximum round capacity of four. The gun's effective range is 150 m.
The KS-23M "Thrush" (Carbine Special 23 mm modernized) was developed on the base of the KS-23. Development for it was started in October 1990. Twenty-five carbines were submitted for testing on December 10, 1991. After which the winner, then designated S-3, became the KS-23M "Thrush" and was accepted for use by the police and the Internal Troops of Russia. The KS-23M includes a detachable wire buttstock and shortened barrel, as opposed to the fixed wooden stock on standard KS-23s. The gun is still chambered in 23 mm. Its overall length with the buttstock is 875 mm, without, 650 mm, and the barrel is 410 mm long. The gun's effective range is 100 m.
The KS-23K is a redesigned KS-23 that features a bullpup layout. The KS-23K was accepted in 1998 for the use of the Russian Ministry of Internal Affairs (MVD). Development and adoption of this carbine was motivated by the fact that in the earlier accepted configurations of the KS-23 and KS-23M a major noted deficiency was that the tubular magazine did not make it possible to rapidly reload or change the type of ammunition being used, because of this a major design change for the KS-23K is that it has an extended box magazine that holds seven shells instead of the three shells seen on the other models. The gun has a mechanical safety located on the left side, above the pistol handle and open non adjustable sights. The gun's effective range is 100 m.
The civilian version of the KS-23 is the TOZ-123 "Drake-4" (???-123 "????????-4"). It is made by Tulsky Oruzheiny Zavod and features a smoothbore design, making it more similar to a traditional shotgun, and is chambered in standard 4-gauge. Since August 1996 it is allowed in Russia as civilian hunting shotgun.
The gun maker's website has this as the description for the shotgun.