I am currently reading a journal article on the Washington D.C. gun ban. The ban, when it was in effect was the most draconian in the nation. Not only would D.C. not license any new pistols, but you literally could not move your gun from one room to another in your own home. And any hope of a self defense clause was so narrow as to be non-existent.
The advocates argued that when you banned the guns in D.C. the murder rate involving handguns would go down. That proved not to be the case. Because D.C. could not extend its jurisdiction outside of its borders, the inflow of illegal obtained guns never ceased. Only a very small percentage of firearms lawfully owned by D.C. residents were ever used to commit crimes while the ban was in effect.
So what good does a ban do if your sphere of lnfluence is is limited, such as Washington D.C. or Chicago Illinois? The law abiding citizens will comply because they believe in the law, good or bad, just or unjust. The criminal who has already rejected the law is not taking that much of a step further in obtaining a banned item. In testimony before Congress the D.C. chief of police testified that seventy nine percent of all homicides in the district involved firearms, yet less than one percent were firearms registered in D.C. The people possessing the other 99% of those guns were be definition, criminals.
The only way gun bans work is in disarming law abiding citizens.