Eleven students from Dylan's class escaped when Adam Lanza stopped to reload his weapon with another 30-round magazine.
"I'm one of those parents who asks myself every day, every minute, if those magazines had held 10 rounds instead of 30, forcing the shooter to reload many more times, would my son be alive today?" she said during a Statehouse news conference. "So please, hear us. Have the courage to stand up for what is right."
Six states - California, Connecticut, Hawaii, Massachusetts, Maryland, and New York - and Washington D.C., have reduced the legal magazine capacity to 10 bullets. At the federal level, President Obama's call to limit magazines to 10 bullets nationwide has not been considered in Congress.
Neither Sweeney nor Republican Gov. Christie supports further restricting magazine capacity in New Jersey. Christie has his own ideas for improving state gun control laws, including toughening penalties for straw purchasers and gun traffickers.
Sweeney, whose district includes Cumberland, Salem, and Gloucester Counties, said the 15-round limit "has been effective."
"What we must focus on now is preventing guns from getting into the hands of those who should not have them," Sweeney said. "That means addressing issues of mental health, background checks, illegal guns, and straw purchases."
The proposal has split the Democratic-controlled chambers in Trenton. The Assembly passed a bill to restrict magazines in February.
"The difference between 15 and 10 could be your child," Assembly Majority Leader Louis Greenwald (D., Camden) said at the news conference Tuesday where he and other lawmakers fought back tears.
Four families who lost children in the Newtown shooting met with Sweeney and a representative from Christie's office Tuesday. They hoped to change their minds.
"Put it to the vote," said Tim Makris, cofounder of the nonprofit group Sandy Hook Promise. "Give people the opportunity to vote yes or vote no."
Majority Leader Loretta Weinberg (D., Bergen) has spearheaded the gun control bills in the Senate. She has separately cosponsored a bill to decrease magazine capacity.
The Senate Law and Public Safety Committee on Tuesday favorably moved gun control bills that would prohibit Internet sales of ammunition, require photos on gun permits, and disqualify those listed on the federal Terrorist Watchlist from buying a gun, among other measures. Many who oppose further restrictions on guns spoke during the three-hour hearing.
Nora Craig, a Navy veteran and farmer from Franklin Township, told the panel it was her job, not that of lawmakers, to defend herself with legally owned firearms.
"If my dogs don't get them, I will," she said of trespassers on her property.
The magazine-capacity proposal was not discussed in committee Tuesday, and the bill is not scheduled for discussion Thursday, when the committee is to consider more gun control measures.
Nelba Marquez-Greene, whose daughter, Ana, was killed at Sandy Hook, said the polarization of the gun control debate frustrates her.
"I can be a proud supporter of the Second Amendment and believe in gun safety," she said.
Neil Heslin, whose son, Jesse, was killed in the Newtown shooting, said it was difficult to watch the Senate this month vote down a measure that would have required background checks for gun purchases.
"Quite honestly, after two trips to Washington, I realized how dysfunctional our government was there," he said. "I mean, there's a lot of pacifying and a lot of doing nothing."
But Heslin said he can't give up.
"I don't think I could live with myself if I didn't try to make a change, just save one life down the road, it's worth every effort," he said.
The families of the 20 children, four teachers, and two administrators killed at Sandy Hook did not pick their mission, but feel it is the only thing they can do.
"Honestly, we would all rather not be here, we would rather have all of our kids home safe and sound," Hockley said. "But what happened happened, and we want to ensure that we do everything that we can to help reduce the opportunity for this to happen again and for other parents to feel this way."
Contact Joelle Farrell at 856-779-3237, firstname.lastname@example.org, or on Twitter @joellefarrel.
This article includes information from Bloomberg News.