Federal prosecutors on Thursday said the operation was run like a drive-thru out of a Philadelphia home, as buyers could drive up and have a gun delivered to their car.
Mayor Rahm Emanuel is seeking to broaden a requirement for gun owners to report the loss, theft or sale of firearms to include all of Cook County.
It's the latest measure aimed at stopping the flow of illegal guns into Chicago, where homicides have risen.
A new Chicago ordinance would also double the jail time to six months for violators, according to a Chicago Sun-Times report.
For the first time, similar reporting requirements would be expanded to all of Cook County under companion legislation that's been drawn up.
County Board President Toni Preckwinkle plans to introduce that legislation at a county board meeting on Wednesday.
Both measures were quickly crafted after an assault weapons ban stalled in the Illinois General Assembly during its lame-duck session.