Found it today. Hope there is enough detail to date it. About 22mm. Any help very much appreciated - thanks!
The inscription (top image) is qian long tong bao which means it was cast during the reign (1736-1795) of Emperor Gao Zong of the Qing (Ch'ing) Dynasty. The reverse side (bottom image) indicates that this cash coin was produced at the Board of Revenue mint in Peking (Beijing). Gary