Specialist police officers were deployed to the Red Lion, Bitterne, on the night of Friday 30 June night after a man was spotted with what was believed to be a handgun.
JD Wetherspoon spokesman Eddie Gershon said a doorman witnessed a man dropping what appeared to be a gun in the pub's garden.
“The member of staff attempted to pick it up, but the male who dropped it picked it up first, then left straight away,” he said.
Gershon stated a second member of the door staff called the police and two armed response officers arrived at the pub.
They looked at the CCTV to get a description of the man and interviewed the door staff.
“The police were very complimentary about the pub team and door staff, and the manner in which the incident was handled,” Gershon said.
“The manager and staff are very well trained and dealt with the situation perfectly, which is backed up by police comments.”
Officers later located and arrested two men at the Robin Hood Pub on South East Road in connection with the incident, and a BB gun was seized, according to Hampshire Police.
William John Mason, 30, Adey Close, Southampton, was charged with possession of a loaded/unloaded air weapon in a public place and is due to appear before Southampton Magistrates' Court on Thursday 20 July.
A 29-year-old man was arrested on suspicion of possession of a firearm with intent to endanger life and possession of an offensive weapon in a public place. He was later released without charge.