Copper 6pdr guns for the Gorcum

I was surprised to see that the Rotterdam ship Gorcum (or Gorinchem) carried two copper 6pdr guns in 1652. The Friesland ship Breda had copper 4pdr guns at the same time. The Admiralty of Friesland had acquired the Breda from Amsterdam, as I recall. Nico Brinck had told me that the "copper" guns were actually made from a composite of iron, lead, and beaten copper. The copper was not cast, but beaten to shape with hammers. As far as I can tell, the Gorcum had the copper 6pdrs replaced by Jun3 1653.