Annan Coastguard and a Royal Navy Bomb Disposal team from Glasgow were called in after a walker spotted the suspect device on the shore near Castle Corner car park.
The team later detonated the object, which was understood to be unexploded World War Two ordnance.
HM Coastguard Kirkcudbright-based senior coastal operations officer Stewart Bryden praised the person who raised the alarm.
He said: “They did exactly the right thing. They did not touched the object, identified the location and immediately contacted the emergency services.”