The most viable effort in decades to stem the flow of guns onto the black market ended with the immunity bill Sanders helped pass.
In the fall of 2005, the city of New York was preparing a mammoth lawsuit against 14 gun manufacturers and 27 distributors and dealers. The suit set out to prove that the gun industry bore a responsibility for the volume of guns illegally trafficked into the city.
To make its case, the city had marshaled significant evidence showing that gun manufacturers were unwilling to take simple steps to keep their guns out of criminals' hands—and even knowingly fed the criminal gun market. The lawsuit highlighted federal data from 1996 to 1998 that had traced more than 34,000 guns used to perpetrate crimes back to just 137 dealers. The Bureau of Alcohol, Tobacco, and Firearms informed gun manufacturers every time a gun used in a crime was traced to their companies, information that would have made it easy for manufacturers to determine which of their distributors and dealers were supplying the black market, yet manufacturers continued to sell guns to those "bad apple" dealers.
As the trial neared, the city had marketing experts, dealers, and former gun industry officials ready to testify that the gun manufacturers' lack of oversight of their dealers and distributors could only be attributed to a willful blindness that allowed them to profit off the criminal gun market. The city's lawyers were prepared to argue that in Southern states with lax gun laws, manufacturers supplied dealers with more handguns than the legal market could consume, knowing the excess guns would be trafficked north up the I-95 corridor and sold illegally in cities like New York.
For the entire story: http://www.motherjones.com/politics/2016/01/bernie-sanders-vote-gun-immunity-black-market
For more on Gun Control: http://gunwatch.blogspot.com