The Grendel R31 is a rare, semi-automatic carbine chambered in .22 Winchester Magnum Rimfire (.22 WMR). Produced by Grendel Inc. between 1991 and 1994, it was designed by George Kellgren, who later founded Kel-Tec. The R31 is essentially the carbine version of the Grendel P30 pistol and is considered the spiritual predecessor to the modern Kel-Tec CMR-30.