The 10mm Magnum is an extended length version of the 10mm Auto and was developed as a factory offered cartridge in the Automag IV pistol around 1992 by ex-California based AMT (Arcadia Machine & Tool Inc), which was later bought by IAI (Irwindale Arms Inc). The 10mm Magnum is basically the rimless version of the old 401 Herters Powermag, It was also touted as a hunting and silhouette cartridge, but ultimately failed as the guns was too heavy and ungainly.