Here's what it says in Krause's Standard Catalog of World Coins Pete:
"The Kingdom of Sweden issued copper plate money, heavy and cumbersome square or rectangular coins ranging in size up to about 13 by 25 inches down to less than 3 by 3 inches, from 1644 to 1776. The kingdom was poor in silver and gold but had rich copper resources. The coins were designed to contain copper bullion in the value of the silver coins they replaced, and were denominated as one, two, four, etc. dalers in silver mint or silver coin.
Although sometimes classed with odd and curious money these were legal tender coins of the realm and although used and exported as bullion, they circulated domestically and were essential in the commerce of Sweden and Finland for more than a century."
Mine was made from cannon bronze but they are also found in copper. The biggest was a 10 daler at almost 20kg. This one's my copper ½ daler from 1743. Unsurprisingly, Sweden were the first country in Europe to introduce banknotes.