Seven rifles and a double-barrelled shotgun were found in a backyard container in Jabulani, Soweto, on Wednesday, police said.
Spokesperson Constable Phindile Mavuso said the Flying Squad and K9 Unit went to the property, responding to a tip-off which police received.
Around noon, they found the eight weapons, as well as 140 rifle bullets and 14 pump-action shotgun bullets.
They had been stashed in a container in the backyard.
Police are trying to locate the property owner, who was not present, to find out what the weapons and ammunition were intended for.
Mavuso said the police valued the efforts of the person who tipped them off.
"We really appreciate it," she said.
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