Obama backs new assault weapons ban

Obama backs new assault weapons ban: "Obama would back proposals to close the "gun show loophole," which allows people to buy weapons without background checks."

What does the research say about how much of a problem this is? What percent of crimes with guns had the gun obtained from a gun show (or any private transaction)?

"We ban about 100 weapons by names"
So if they just change the name then the weapon is ok? It seems illogical to ban by name. The only benefit that I can see is political.