Detectives from Organised Crime Branch found the gun and 3.5kg of drugs worth £70,000 at the property in the Rathenraw area of the town on Tuesday.
Two men aged 29, were arrested and are currently being questioned at Antrim police station.
The searches were part of an ongoing investigation with Border Force officers into the alleged importation and supply of Methedrone and money laundering offences.
Neill Kelly, Alliance Councillor for the area, said that while it is worrying to hear of this type of find in the Antrim area, the streets are certainly safer for it having been discovered and removed.
"PSNI officers are working effectively to address all types of crime in the area and the local community is very important in ensuring this continues," he added.
"I would urge anyone with information about matters relating to drugs or other crimes to contact the police immediately."