Gunmoney.

Gunmoney (sometimes "Gun Money") was coinage issued by James II in 1689 and 1690, struct from metal obtained from obsolete field cannons (hence the name).

The story was basically this: when Charles II died with no legitimate heir to his throne, his brother James II was crowned king. When William, the Prince of Orange in the Netherlands, took over the English throne, James fled to France, gathered an army, and returned to Ireland in order to retake his throne.

Short on funds, James minted his own coins - using melted metals from cannons (and actually from other metals like cooking pots and pans) - to be redeemable in sterling, if and when he regained his throne (which he never did, because he was defeated by William in the Battle of Boyne River).

Link | Gunmoney [wiki]