The MK II (“Mark Two”) was made from 1982 to 2005. It replaced the Standard, Ruger’s first model, made from 1949 to 1982, and the MK I Target, made from 1951 to 1982. The MK II was removed from production in 2004, when it was replaced by the MK III. All Ruger rimfire pistols are chambered in .22 Long Rifle only.