From a story on the BBC, Fragments from at least 2 different guns were found by metal detector at an old battlefield in Towton, England.  This was the earliest battle on record where handheld firearms were found in England.  The Battle of Towton was fought during the War of the Roses and at least 28,000 men died that day.  The fragments were exposed to neutron analysis and were proved to be from 2 different guns, and were probably blown up also.  According to archeologist Tim Sutherland, casting of guns was unreliable in those days ( and for many days after that ) and the guns were more dangerous to the shooter than the enemy.  There were traces of gunpowder founds on them as well.

gun fragments