No injuries were reported by the FBI.
It happened Monday afternoon at Southwest Federal Credit Union on West Gore.
The FBI says the man was wearing a gray hoodie, dark gloves, a dark ski mask, and dark sunglasses.
The man approached two tellers with a handgun and demanded money be put into a plastic grocery bag. While a teller was putting money into the bag, the man's gun discharged, hitting the bag.
The robber then fled the scene on foot, with some of the money spilling out of the bag.
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