Police found a semi-automatic pistol, ammunition, a magazine and a silencer during a raid at a Crossley property on Monday morning.
Detective Sergeant Andy Raven, of the Warrnambool police crime investigation unit, said a warrant was executed at a Crossley property soon after 8am.
"Officers located a semi-automatic pistol, silencer, magazine and ammunition," he said.
"The investigation remains ongoing to identify offenders involved."
Police have arrested and charged a 47-year-old Warrnambool man with being a prohibited person possessing a firearm.
Anyone with information about illegal firearms is requested to contact their local police station or Crime Stoppers on 1800 333 000.
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