The earliest european cannonry was made of bronze, but it was expensive and the raw materials were not readily available. From the 15th century onwards, attempts were made to use cast iron instead. In spite of its gradually increasing use there was considerable prejudice against it, because of its failure rate. Cast iron burst and the fragments could kill or maim everyone within range. The technological factors involved in this problem are considered and an attempt made to determine how high in practice was the cast-iron failure rate. One factor may have been economic: iron foundries are expensive and have to work continuously. Lack of practice in weapon manufacture, through intermittent manufacture of non-bellicose items, may have been responsible in part. Tables, drawings, references.