"How many massacres until somebody says it's not worth it anymore?" asked the families' attorney, Josh Koskoff.
If the victims' families are victorious, it would be both a legal and cultural landmark. And it comes barely a week after a gunman armed with a similar semiautomatic weapon gunned down 49 people in a gay nightclub in Orlando
"As I heard the news about Orlando [I felt] sadness, grief, disgust...No one should ever be put in that position," said Matthew Soto, whose sister Victoria Soto was a Sandy Hook teacher.
Adam Lanza was armed with a Bushmaster XM-15 on December 14, 2012, when he killed six adults and 20 children, ages 6 and 7, at Sandy Hook Elementary School in Newton, Connecticut.
"A weapon that was designed to be used in combat and to kill enemies in war...was lying not on a battlefield but on the floor of Vicki Soto's classroom," Koskoff said. "How did it get there?"
A highly unusual suit
Typically, gun manufacturers can't be sued when their products are used to commit a crime. But the families' suit argues that AR-style guns serve no legitimate purpose in civilian hands and therefore the gun maker shares culpability for the Sandy Hook killings.
The suit also argues that Bushmaster's manufacturer intentionally used military language in its marketing to appeal to people eager to acquire a weapon capable of mass murder.
But the legal team representing Bushmaster, Remington, and other companies associated with distribution and sale of the weapon argue that they are not responsible
for Lanza's crime because they didn't directly give him the weapon.
Officials have said Lanza got the weapon from his mother, who he killed before going to Sandy Hook Elementary.
"The firearms were used by Adam Lanza. It wasn't used by Nancy Lanza," argued Remington's attorney, James Vogts.
The defense also repeatedly brought up the 2005 Protection of Lawful Commerce in Arms Act, or PLCAA, which grants gun manufacturers immunity from any lawsuit
related to injuries that result from criminal misuse of their product.
It's up to lawmakers to change the law if they choose, Vogts said.
"This is clearly a legislative issue," he said, "and not an issue for this courtroom."
Judge Barbara Bellis denied the defense's motion
to dismiss the case in April. Now attorneys for the gun makers are trying again to get it tossed. Bellis has already set a 2018 trial date in the lawsuit.
'How many more massacres?'
Heading into court, Koskoff evoked the Orlando shooting and the gunman's use of an AR-15-style rifle. He also named other recent mass shootings in which powerful guns were used.
"How many more San Bernardinos? How many more Auroras? How many more Orlandos? And probably in six months we can add another one to the list until the Remingtons of the world say, 'You know what? It just isn't worth it anymore,'" Koskoff said.
In court, he told Judge Bellis: "The AR-15 is the most dangerous, most lethal instrument readily available to the civilian population." He added that the U.S. military considers the gun its "weapon of choice."
"It was Remington's choice to entrust the most notorious killing machine to the public," which constitutes negligence, he argued.
The families are asking for unspecified damages. When reporters have challenged the families' attorneys to be more specific about what they want, they've repeatedly said their clients want accountability.
Koskoff stressed that it's not the goal of the suit to "ban anything."
"That is the lawmakers' role," he said.
If the suit goes forward and the Sandy Hook families win, it would be a hit on the companies' bottom lines, Koskoff said, but that doesn't necessarily mean they will make changes.
Judge Bellis is currently weighing both arguments and could rule at any time.