The Second Amendment protects the right of all citizens to keep and bear arms but like any other legal right it has its limits.
Those limits have been clarified several times by the U.S. Supreme Court, most recently in 2008. But the development of new and more sophisticated weaponry opens up the possibility for renewed investigation.
Justice Antonin Scalia, whose decisions generally favor gun rights, told Fox News that Second Amendment rights are certainly limited although he didn't elaborate how. To speculate on what he might have meant, it's helpful to understand what limits already exist.
U.S. v. Heller
The most recent decision on Second Amendment rights, U.S. v. Heller, prohibited any kind of complete ban on a category of guns.
At issue was a D.C. law banning ownership of any handguns. That law was struck down and the decision effectively barred states from implementing similar laws.
No state can take it away your Second Amendment rights. But they can place limits on it.
The way most states regulate guns is through licensing requirements and bans on certain guns within a given class. Those kinds of limits have generally been upheld by courts and Heller doesn't stop them.
That means state assault weapon bans and restrictive license and permitting laws are generally acceptable limits on Second Amendment rights.
Regulations on Fully Automatic Weapons
One of the more famous examples of highly restrictive gun laws is federal regulation of fully automatic weapons or machine guns.
Machines guns aren't banned in the U.S.; Heller likely wouldn't allow it. But they are subject to intense regulation. Under the National Firearms Act, prospective owners must apply to the U.S. Treasury Department for special permission to own machine guns.
Applicants undergo rigorous screening by the FBI. If granted permission, owners pay a tax and must register their weapon with the federal government.
The Firearms Owners' Protection Act of 1986 then made it illegal for civilians to own machine guns made before the act's passage on May 19, 1986.
Unless the Supreme Court says otherwise, this kind of regulation is a legitimate limit on Second Amendment Rights. While an outright ban isn't legal, strict regulation that creates an effective ban is still acceptable.