Abstract: An amorphous metal alloy strip is disclosed having a width greater than about one inch and a thickness less than about 0.003 inch, this alloy consists essentially of 77 to 80 atomic percent iron, 12 to 16 atomic percent boron and 5 to 10 atomic percent silicon with incidental impurities. The strip has a 60 cycle per second core loss of less than about 0.100 watts per pound at 12.6 kilogauss, saturation magnetization of at least 15 kilogauss, and a coercive force of less than about 0.04 oersteds. Such alloy is further characterized by increased castability and the strip produced therefrom exhibits at least singular ductility. A method of producing such optimum strip is also disclosed.