The 6x51 Atzl was designed by the gunsmith Andy Atzl from Kaufstein in Austria. The 6x51 Atzel was intended for hunting and sport usage. Brass are available from both Hirtenberger and Hornebner. 

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.