Congress didn't pass new gun-control laws. Now state legislatures from Colorado to Maryland are trying. Can states do anything that actually works?

I posed that question to three public-health experts: David Hemenway of Harvard University, Andrew Papachristos of Yale University, and Eugene Volokh of the University of California, Los Angeles.

States can make up for inaction by the federal government -- but only partly, Hemenway told me. A state-by-state approach is most promising for reducing gun suicides and accidents. "These are almost always home guns, so local policy matters a lot," he told me.

On the other hand, the power of states to regulate guns has a practical limit: You can transport a firearm across state lines. State restriction against gun acquisition by felons or a state mandate for background checks would have little traction as a result. "To be sure," Volokh said, "there are some things that simply won't work if not at the federal level."

Guns used in crimes are sometimes local, but usually not. An overwhelming share of gun crimes in Canada, Mexico and Jamaica are accomplished with American guns, Hemenway told me. "From the viewpoint of someone in New York or Massachusetts, we can have stronger gun laws, but their effect would be mitigated because people can bring guns from areas with weaker rules," he said.

Papachristos concurs. "I did work on Chicago's gun laws, and one reason why they didn't work is because of other states' lax laws," he said. Chicagoans are only a few highway exits from Indiana, where gun laws are far more lax. The distance isn't a sufficient barrier for gun crime, no matter how strict Chicago's laws.

There is a case for our gun-law federalism. Blue states are tightening their rules without dragging the gun-happy South and West along for the ride. Americans will see what works and what doesn't.­

This isn't be the first time states have led on a policy issue better suited to federal action,. The Northeast has run its own cap-and-trade program, the Regional Greenhouse Gas Initiative, for a decade. Northeastern states could conceivably coordinate a tightening of gun laws, too.

"One of the great things about having fifty states is that you can experiment. That's true in gun policy too," Hemenway said. "We don't know enough about what laws will really make a difference. If two states are otherwise similar, but one changes their laws and the other doesn't, that's good for gun-policy research."

Getting more data would be a big deal, said Papachristos. An amendment written by former Kansas Representative Todd Tiahrt that limited access to government data on guns has crippled empirical work for the last decade.

What the research suggests so far is that state regulations might prevent some gun suicides and accidents. Unfortunately, it's probably still up to the federal government to deal with gun crime.

(Evan Soltas is a contributor to the Ticker. Follow him on Twitter.)