MTs 21-12 (known as MC 21-12 in export grade; Russian МЦ 21-12) is a Soviet/Russian semi auto shotgun. It was designed in TsKIB SOO and manufactured mostly by TOZ; over 300,000 were produced. The first version of MTs 21 was produced in small numbers for less then a decade and chambered for 12, 16 and 20 gauge, while main production version MTs 21-12 from 1965 was chambered only for 12/70 cartridges.