Bartlett was just posturing after Badger Outdoors just outside Milwaukee proper came up as the #1 crime trace store in the US again this summer. The fact that Badger manages to stay in business with such a dubious distinction shows how closely they flollow the laws, and they bend over backwards to work with the police and ATF.
Badger then made the news by publicly screwing WI gun owners a bit by saying they would welcome such a law. Which of course they would, since as an FFL, they can't sell to 18 year olds anyway, and they would stand to gain economicaly from FFL fees if face-to-face private sales were to become illegal in WI.
As mayor of Milwaukee Barrett has no input in state law other than his high profile to speak his mind and hope a like minded legislator would submit such a bill. The legislature is not even in session, and there are no bills for consideration at this time.
Considering that we consistently fell only one or two votes shy of the 2/3rds supermajority on CCW here in WI if he had a sponsor for such a bill, even if it existed, is going nowhere fast.
With state gun-law pre-emption, Milwaukee can't even pass a city ordinance on the matter.