Introduced in 1959 by Winchester, the .22 Magnum round is the most successful rimfire round that came out in the 20th century. As a larger case than the 22LR, the 22 Magnum is generally loaded with rounds with a 40 grain weight. Other names for the 22 Magnum include the 22 WMR, .22 Mag, and 5.6x27mmR.