About the Manufacturer:
Arcadia Machine & Tool, or AMT, was a firearms manufacturer from Irwindale, California that produced a line of pistols using the name AutoMag from 1982 to 1995. These semi-automatic pistols carried a name similar to the sole pistol model that the defunct Auto-Mag Coproration had previously produced. But, there is no connection other than the name similarity.
AMT did not fare well in business and eventually went bankrupt. AMT's assets and trademark were sold off and they passed between a couple of different companies until they were finally acquired by the High Standard Manufacturing Company of Houston, Texas. High Standard still produces various models under the AMT brand, based on original AMT designs.
About the Cartridge:
This cartridge was introduced by Winchester in 1979 to be used in the gas-operated Wildey pistol. Winchester's new pistol was not much of a success, but the powerful .45 Wincheter Magnum cartridge was. The cartridge is essentially an elongated version of the .45 ACP round. It was the most powerful semi-auto cartridge of its time, until the introduction of the .50 Action Express in 1988.