WASHINGTON — One of the first votes cast by Democratic Sen. Martin Heinrich was against legislation from Sen. Dianne Feinstein to reinstate an assault weapons ban in the aftermath of the Sandy Hook school shooting.

In the decade since, as mass shootings have touched almost every corner of the United States, the senator, an avid hunter once endorsed by the NRA, has been considering what it would take to draft legislation that avoids banning guns that Americans use for legitimate purposes while still saving lives.

He has also watched his two sons grow up learning how to hunt as well as how to duck and cover in mass-shooter drills that bring him to tears.

“I think there’s a generational shift happening,” Heinrich said in an interview with The Associated Press.

“It really made those of us who grew up inside gun culture reevaluate our views and think hard about, like, this is not a black and white issue,” he said. “You can accept the fact that guns are a legitimate tool without accepting that you should be able to own firearms that are really designed to inflict mass lethality.”

The outcome is a new iteration of gun violence legislation from Heinrich and Sen. Angus King of Maine that focuses on what are often referred to as assault-style weapons, which are among some of the most popular in America, and zeroes in on the part of the gun that makes them especially dangerous in mass shootings.

Rather than try to ban assault weapons outright, their legislation would essentially regulate such guns to have permanently fixed magazines, limited to 10 rounds for rifles and 15 rounds for some heavy-format pistols. The idea is to reduce a shooter’s ability to fire off dozens of rounds in seconds and prevent them from being able to attach a new magazine to keep shooting.

The senators come from rural states where guns are popular, and their legislation would allow gun owners to keep existing guns but would also create a buy-back program, among other provisions. It’s called the Go Safe Act, named after the internal cycling of high-pressure gas in the firearms in question.

“Both of us were uncomfortable with an assault weapon being defined by its appearance because that can be manipulated, and we were looking more functionality,” said King, whose state recently endured the worst mass shooting in its history when a gunman shot up a Lewiston bowling alley and bar leaving 18 dead and many others injured.

“Lewiston, certainly for me, brought home how important it is,” said King, an independent who caucuses with Democrats, to AP. “It sort of strengthened my resolve.”

The National Rifle Association opposes the legislation as “the most sweeping gun prohibition bill of the 21st century.”

Randy Kozuch, executive director of the NRA’s Institute for Legislative Action, said in a statement that the bill would ban “the very types of firearms and magazines most often utilized by Americans for defending themselves and their families.”

He said the bill “blatantly violates” the U.S. Constitution and Supreme Court rulings.

Fourteen states and Washington, D.C., have their own bans on large-capacity magazines, according to the Giffords Center to Prevent Gun Violence, though those laws are facing new court challenges in the wake of a 2022 Supreme Court ruling that’s led to widespread upheaval in the nation’s firearm-law landscape.

But Mark Collins, director of federal policy at Brady, the gun violence prevention organization, said this new approach, focused on the gas-operated mechanism and the nondetachable magazine, is unique. The time it takes to stop and reload, he said, is often the “critical moment” when a mass shooter can be stopped.