Chicago is tough. It has a ban on gun shops, a ban on "assault weapons and high-capacity magazines," and no civilian gun ranges. So where did a big chunk of the 50,000 guns the police recovered and traced between 2001 and 2012 come from? Beyond the city's borders:

[M]ore than 15,000 of the guns traced by the police came from just outside the city limits in Cook County and in neighboring towns that permit gun stores.
Altogether, nearly half of the guns came from locations around Chicago. What does this mean? An effective ban can only be a universal ban.