WASHINGTON (CBS / AP) — Connecticut’s two U.S. senators are joining forces with California Sen. Dianne Feinstein and other key senators, proposing a retooled federal ban on assault weapons in the wake of the deadly Newtown school shooting.

Sen. Richard Blumenthal told The Associated Press on Wednesday that the proposed legislation, to be unveiled Thursday in Washington, D.C., will more narrowly define what’s considered an assault weapon under a resurrected ban. The bill, he said, will also prohibit high-capacity magazines, limiting them to a capacity of up to nine rounds of ammunition.

Blumenthal said the legislation is “one of the most significant” bills to be introduced following the Dec. 14 massacre at Sandy Hook Elementary School. It also marks the first bill that Blumenthal and Sen. Chris Murphy have worked on together as senators.

“This bill will be a signature moment in providing a profoundly significant step in the legislative strategy,” said Blumenthal, adding how final language of the bill was still being drafted on Wednesday. “But it is only a first step and we need to build on it with a comprehensive program” that includes expanded background checks and mental health care.

President Barack Obama has also proposed reinstating the federal assault weapons ban, which Congress failed to renew in 2004. Senate Majority Leader Harry Reid has said such a ban might clear the Senate but doubts it could pass the House of Representatives. Obama has also proposed renewing a 10-round limit the size of magazines.

Robert Crook, a state gun rights advocate and executive director of the Coalition of Connecticut Sportsmen, said assault weapons bans, such as the one in Connecticut, have not accomplished anything.

“All it does is impact the legitimate citizen and has no relevance to crime control and atrocious incidents like Sandy Hook,” he said, adding how American gun manufacturers “know how to innovate” and have been able to get around the state’s ban.

“What legislators should do — if they’re going to do something — they ought to come up with something innovative that both benefits the citizen and doesn’t impact the citizen, and benefits crime control,” Crook said.

Murphy, whose former House district includes Newtown, contends that a tougher assault weapons ban will save lives. He said the revised ban that’s being introduced Thursday will be difficult for manufacturers to skirt and would ban the type of AR-15 rifle used by the shooter in Newtown.

“If this bill had been in effect, there would be little girls and boys still alive today in Newtown,” said Murphy, adding how the only inconvenience to sportsmen would be reloading more frequently at shooting ranges because of the smaller magazines.

“This bill is the bread and butter of gun reform,” Murphy said. “If you get military rifles and high-capacity clips off the streets, there are going to be less people killed in mass shootings going forward. It’s as simple as that.”

Blumenthal said the bill defines rapid fire assault weapons in terms of a single feature, such as having a pistol grip or a flash suppressor. Connecticut’s ban defines the weapons in terms of having two features.

Murphy and Blumenthal are scheduled to unveil the details of the bill with Feinstein and Sens. Dick Durbin of Illinois and Chuck Schumer of New York during a news conference. Also, U.S. Reps. Carolyn McCarthy of New York, a leading voice in Congress in favor of gun control, and Ed Perlmutter who represents Aurora, Colo., where a gunman opened fire in a movie theater last year, are scheduled to be on hand, along with gun safety advocates, law enforcement and teacher organizations, Blumenthal said.

The Dec. 14 shooting in Newtown left 20 first graders and six educators at the elementary school dead. The gunman also killed his mother at the home they shared and eventually took his own life as police arrived at the school.

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