Better background checks for gun purchases would be a start, with a national database.
I think the idea of focusing on guns is a bit silly for a variety of reasons. But on the topic of murder? Guns are already out there. 310 million or so. And it doesn’t address the root cause. New York City saw like an 80% reduction in murder. We have a unique issue in that 65% murder is concentrated to 157 counties. That is south of 10,000 murders and above 9000 in 157 counties. Which IS impressive for a population of 325 million. But still.
Imagine if we saw even a 50% reduction? Or 30% in those counties? You are talking about 11,000 murders in a population of 325,000,000. 3.3 per hundred K? Not much to sneeze at.