In terms of what we could do to get that number down, there is probably more evidence that aggressive stop-and-frisk would do more to reduce that number than banning assault rifles(see NYC experience).

However, even if there is evidence that stop-and-frisk would reduce the number of gun murders, there are still serious Constitutional issues mainly in that the vast majority of people stopped are innocent. In the same way, the vast majority of guns and gun owners will never be involved in any crime. Thus any tightening of gun laws will affect far more innocent people than actual criminals.