Officers stopped the black Mazda 6 on Sauchiehall Street on Friday evening as part of an intelligence-led operation.
A 55-year-old man has been arrested and he will appear at Glasgow Sheriff Court on Monday, Police Scotland said. A report is being submitted to the procurator fiscal.
As part of the same investigation, a red Volkswagen Golf was stopped and searched by armed police in Neilston Road, Paisley, later on Friday night.
No items were recovered and no-one was arrested
Detective Inspector Martin McGhee of Police Scotland's specialist crime division said: "As part of an ongoing investigation, officers from Police Scotland have recovered a firearm and ammunition.
"I would urge anyone who may have information about the criminal use of firearms to contact Police Scotland on 101 or, alternatively, the charity Crimestoppers anonymously on 0800 555 111."
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