Army experts were summoned to Magilligan yesterday to examine a number of suspicious objects on the Lough Foyle shoreline.
The objects had been reported by a member of the public.
The PSNI said in a statement: "A number of training rounds were discovered on the loughshore at Scotchtown Road and were subsequently examined and seized."
Magilligan is home to an Army firing range and training camp. There has been a firing range there since the Napoleonic Wars, according to the Army.
In recent years, nationalist politicians have called for it to be closed, as they say it harms tourism in the North West.
Munitions regularly wash up on Northern Ireland's beaches - but mostly in the north east, closer to Beaufort's Dyke, an Irish Sea trench where well over a million tonnes of ordnance was dumped after World War Two.