There's something like 2500 federal, state, and local firearm laws and ordinances. Murder is already illegal. So is selling guns without an FFL in some states. NY state enacted some of the toughest gun laws last year and it's already nigh on impossible to legally own handguns in NYC.
The market for illegal guns in already there among criminals. Making it harder for law abiding citizens to get guns doesn't make it harder for criminals to get illegal guns (see also: drugs). All it does is make it harder for the law abiding citizen.
Instead of further restricting the 100,000,000+ gun owners who won't commit a crime., how about we just make violent criminals stay in prison?