Police believe the shotgun cartridges found on Upper Cheung Sha beach most likely fell off a passing boat.
After initially finding 19 shells last weekend, a search by police and LCSD cleaning staff located another eight.
A police spokesman said the recovered unused shells were increasingly rusty – a sign they had been in the water for some time.
The unused shells, made by Italian firm RC Cartridges, have undergone forensic analysis but police have have been unable to determine their source.
“They probably fell off a boat, accidentally or otherwise,” the spokesman said.