He's dedicated the past 13 years to urging politicians to pass stricter gun laws. Experts say the effort has been largely unsuccessful.
Part of the reason for that rests with the troubled ban on assault weapons that passed in 1994 and was due to last 10 years. It expired in 2004 during President George W. Bush's administration. The specifics of that ban were complicated, critics said, which allowed for numerous loopholes. It also only applied to new gun purchases.
Further, gun-control advocates are up against the National Rifle Association, which has 4 million members in the United States.
This year, the NRA spent $17 million on federal elections. Annual gun sales in the United States total about $3.5 billion, according to CNN Money.
"It's not like the NRA represents some tiny splinter of American culture," said Paul Barrett, author of "Glock: The Rise of America's Gun."
"The liberal argument is that the NRA distorts democracy or bullies politicians. That's not true. They don't speak for cosmopolitan circles on the East or West Coast or the mayor of big cities," he said. "They don't speak for populations of people who are affected by urban crime. But they do speak for many, many people who have guns and don't want those guns taken from them."
Barrett said he feels compassion for everyone in Newtown. But Newtown United is entering a fight tougher than they could possibly fathom at this stage, he added.
"They are entering into a very ideologically charged arena, and are going to run up against a very cynical, very complicated and well-practiced maelstrom," he said. "I wish them the best but I would be surprised if they don't end up quite disillusioned having watched this process."
Start with talking
Shull appreciates that.
Neither he nor Murray have had the time in the past 72 hours to dive into the language of the ban on assault weapons, they said.
But they want to, and intend to.
While Shull said Newtown United wants to also address loopholes in mental health care and making schools safer, he stressed that the group generally is focused on one objective. They think it's achievable in the short-term. They want to sit down and talk to people who support gun rights.
"We have to sit down as adults and have an open dialogue and listen to that other person and find that middle ground," Shull told CNN.
At least two politicians who were for gun rights, Democratic Sens. Joe Manchin of West Virginia and Mark Warner of Virginia, said they would weigh supporting new proposed limits on firearms.
The NRA has been silent, though Tuesday afternoon it announced it will hold a press conference Friday. Its Facebook page has been deactivated, and visitors are redirected to a bare-bones page where comments are disabled (although "Likes" are still allowed). Its Twitter account, which typically posts several times a day, also has been quiet. The group's last tweet, on Friday morning, was a promotional message that said, "10 Days of NRA Giveaways -- Enter today for a chance to win an auto emergency tool!"
An advocate for Newtown?
Shull said there's hope within Newtown United that they'll have a major prizefighter in their corner -- Sen. Dianne Feinstein, D-California. She was one of the major backers of the 1994 assault weapons ban.
Feinstein said she'll introduce the bill when Congress reconvenes in January and the same legislation will also be proposed in the House of Representatives.
It will ban the sale, transfer, importation and possession of big clips, drums or strips that contain more than 10 bullets, she said.