A member of the public found the device at Corsewell Point area on 18 May and reported it to the coastguard.
A cordon was placed around the unidentified object while coastguard members from the Belfast and Stranraer teams took pictures of the scene and gathered information for the Royal Navy Bomb Disposal Team.
The following day, specialist officers from the bomb squad moved the device to a safe place in Lady Bay before carrying out a controlled explosion.
The teams then stood down and returned to their stations at about 2pm on 19 May.
A video published on the Stranraer Coastguard Facebook page shows the controlled explosion taking place at Lady Bay.
A coastguard spokesman added: “If anyone finds anything on the beach that they think could be ordnance then please do not to touch it and call 999 and ask for the Coastguard.”