Chicago's handgun ban
Chicago's attempt at banning handguns makes that of DC look like a success.
Of course to the city government that's just proof that if there was more regulation of private firearms, it'd work even better. I recall once reading an advocate of Prohibition, after its repeal, still arguing that it would have work if just there had really been a complete ban on alcohol. I forget now what the exceptions were (all tightly regulated), I know there was one for religious services, may have been others for medical use or industrial uses. The author was convinced that these kept the "idea" of alcohol alive and if they'd just have been cut off then the Great Experiment would have succeeded. Sure, Al Capone would have felt a moral duty to straighten out.