The basic technology behind muzzle-loading artillery did not change very significantly between the late 16th and the early 19th centuries, but throughout the period there were attempts to improve both the accuracy and the safety of guns and gunfounding. The Royalist cavalry general, Prince Rupert, was involved in one of these attempts while enjoying a quiet retirement as Constable of Windsor Castle after the Restoration of his cousin, King Charles II. In 1671, he obtained a patent for a secret process, whereby cast iron cannon could be made 'as handsome and convenient as brass ones', but also lighter and, most importantly, cheaper. The monograph traces the story of these guns, through a myriad of contemporary documents to the surviving guns themselves, describing the financial, administrative and social ramifications of this episode which are revealed in fascinating detail. It also lists the total number of these guns into the Ordnance Office stores, giving their sizes and weights.