(Updated at 3:45 p.m. Eastern to add comment from Lautenberg's and McCarthy's offices.)
By Michael Isikoff
NBC News National Investigative Correspondent
Sen. Frank Lautenberg, D-N.J., and Rep. Carolyn McCarthy, D-N.Y., with the backing of gun control groups, are drafting a bill that would ban the sale of high-capacity magazines such as the one that was used allegedly Saturday by Jared Lee Loughner, the man accused of murdering federal Judge John Roll and trying to assassinate Rep. Gabrielle Giffords, D-Ariz., according to two gun control activists working with McCarthy's staff.
Gun control proponents are hoping to move rapidly on the measure in the wake of reports that Loughner's access to high-capacity, 33-round magazines substantially increased the lethality of his attack, the activists said. An Arizona law enforcement official confirmed to NBC News on Monday that Loughner had actually gotten off at least 31 shots during the Saturday shooting, not the 20 that were first reported. He was emptying his first high-capacity magazine and was trying to reload with another high-capacity magazine (with another 30 rounds) when he was wrestled to the ground, the official said.
"In the wake of these kind of incidents, the trick is to move quickly," said Kristen Rand, legislative director of the Violence Policy Center, one of the gun control groups working with McCarthy's office.
McCarthy, one of the House's strongest gun control proponents, whose husband was killed in a mass shooting on the Long Island Railroad in 1993, confirmed Sunday that she was drafting a new bill in the aftermath of Tuscon .an aide said her office was consulting with other members, including House Speaker John Boehner's office, and that she hoped to have draft language as early as this week. A Lautenberg aide said Lautenberg was working on a similar version in the Senate.
"The only reason to have 33 bullets loaded in a handgun is to kill a lot of people very quickly. These high-capacity clips simply should not be on the market," Lautenberg said. "Before 2004, these ammunition clips were banned, and they must be banned again. When the Senate returns to Washington, I will introduce legislation to prohibit this type of high-capacity clip."
Lautenberg was referring to an issue that has been highlighted in recent days by senior federal law enforcement officials: the manufacture of the kind of high-capacity magazines the suspect had with him at the Tucson shopping mall was barred under a federal assault weapons ban that was passed by Congress and signed by President Bill Clinton in 1994.