The 18,5 KS-K (18,5 КС-К, Карабин Специальный, с Коробчатым магазином, Karabin Spetsial'nyy, s Korobchatym magazinom, Special carbine with box magazine) is a Russian semi-automatic shotgun.
The 18,5 KS-K was designed to cater to law enforcement units, self-defense purposes and the like. However, the KS-K is quite unpopular with Russian police units, due to the lack of specialized 12 gauge shells available in the area and that most police officers in Russia much prefer to use submachine guns or assault rifles as opposed to shotguns.
The 18,5 KS-K heavily resembles a normal Kalashnikov rifle or a Saiga-12; in fact, the KS-K uses a modified Saiga-12 action with a rotating bolt. However, unlike the Saiga-12, the KS-K's gas system cannot be adjusted. Also, unlike the Saiga-12, the KS-K has a bolt hold-open system, where the bolt is locked back when all rounds are expended; as the weapon lacks any form of dedicated bolt release system like a lever or a button, the charging handle must be pulled back and then released to cause the bolt to fly back forward.
The KS-K has a hinged, top-opening receiver cover, similar to most AKs and derivatives of the AK, although the KS-K has an additional Picatinny rail installed on top as standard. The weapon apparently uses unmodified AK-74-styled sights. The weapon has a side-folding buttstock. A plastic magwell is provided to allow for faster reloads, similar to the older AK-12/76 shotgun prototype.
- Despite it being considered a "carbine" according to its Russian name, the 18,5 KS-K is actually a smoothbore shotgun; the reason as to why it is classified as a carbine despite lacking rifling is unknown.