OverviewThe KS-23 or Karabin Spetsialniy 23 is a Russian Shotgun that uses a unique cartridge. It loads a 23x75mm rimmed shotshell. The other names of this shell would be 6.278 Gauge, and .906 Bore. The shotgun was created by TsNIITochMash for the Russian Ministry of Internal Affairs (MVD). Originally to be used for suppressing prison riots, the KS-23 remains in use today with Russian Law Enforcement.
The barrel of the KS-23 are flawed barrels from a ZSU-23-4 Shilka, these barrels are unfit for use in the SPAAG unit, but deemed acceptable for the lower stress of firing slugs and less-lethal ammunition. These barrels were then cut down for the KS-23.
KS-23M "Thrush" is a modernized KS-23. Development started in October 1990. 25 of these were submitted for testing along side other shotguns on December 10, 1991. The winner would be designated S-3 and put into service by the Police and MVD. The KS-23M won the tests.
The KS-23K redesigned the KS-23 into a bullpup design. It was accepted in 1998 for use with the MVD. It used elements from both the KS-23 and KS-23M. It has an extended box magazine with 7 shells instead of 3 in a tube.
The Civillian version of the KS-23 is the TOZ-123 "Drake-4". It is made by Tulsky Oruzheiny Zavod and features a smoothbore design, making it more similar to a traditional shotgun. It is chambered in 4 Gauge. Since 1996 it is allowed in Russia as a civilian hunting shotgun, however it is banned in the United States.
Tulsky Oruzheiny Zavod's site description
The shotgun is multicharged, with a tubular underbarrel magazine of 3-cartridge capacity. Reloading is provided with a removable fore-end. The presence of the special barrel rear projection on the frame combined with the rear sight gives the possibility of mounting an optical sight. The shotgun is intended for the amateur hunting with shot cartridges.