June 18th, 1815. English musket ball from the Waterloo battlefield. ex: Waterloo Museum, Broadstairs, Kent, England, with certificate of authenticity. The Waterloo Museum was founded by Derek Spaulding who visited Waterloo numerous times and conducted archaeological exploration as well as collecting artifacts that had descended in the families of locals. Perfect “drop” as the field was mud that day. About .68 cal. From the Waterloo Museum.