Sen. Martin Heinrich (D., N.M.) called for "common sense" gun reform Thursday, saying he wanted to increase the minimum age requirement on the purchase of semiautomatic rifles and "gas-assisted receiver firearms."

Heinrich did not elaborate on the latter category, the meaning of which is unclear. He did, however, express support for a wide range of gun control measures, including age minimums and banning the sale of guns to those on the no-fly list.

"There are a couple of things I can think of that I think are possible now," he said. "Increasing age limits: Certainly somebody who's 18, 19, 20 years old shouldn't be able to purchase an assault rifle, an AR-15, or other gas-assisted receiver firearms when they can't buy a simple handgun, so that should be changed."

The term "assault rifle" is an ambiguous term sometimes used to refer to fully automatic rifles, semiautomatic rifles, or a select group of rifles classified by cosmetic features that make the gun resemble a "military style" weapon. Fully automatic weapons are already illegal for new sales to civilians in the United States. Preventing those under 21 years of age from buying an AR-15 is an idea gaining in popularity, with supporters including Fla. Gov. Rick Scott (R.) and President Donald Trump.

Gas-operated autoloaders were invented in the 19th century and are a common feature of rifles, including the AR-15, but there is no such thing as "gas-assisted receivers." A receiver, sometimes called a firearm frame, holds internal components.

Heinrich went on to endorse the "no-fly, no buy" provision proposed by Sen. Susan Collins (R., Maine) in the Terrorist Firearms Prevention Act. The provision would prohibit people on either of two terror watch lists—the no-fly list and the selectee list—from purchasing firearms.

"I also think the ‘no fly, no buy’ provisions that I've worked on with Senator Collins of Maine, that's a very common sense thing," he said. "If you can't get on a commercial airliner because you're too dangerous, you shouldn't be able to walk into a sporting goods store and buy a semiautomatic rifle."

Civil-rights groups have criticized "no fly, no buy" rules because they treat people differently based on nontransparent government lists. The lack of clarity over the lists poses problems for the due process of law, something Trump said could "come second" for law enforcement when seeking to confiscate firearms in certain cases.