WASHINGTON -- Pennsylvania Sen. Bob Casey, who changed his stand to favor new gun laws following the Sandy Hook school shooting in December, is going one step further.
Casey has signed on as co-sponsor of New Jersey Sen. Frank Lautenberg's bill to limit gun magazines to 10 rounds or fewer.
"As members of the U.S. Senate we must ask: have I done enough to reduce the likelihood that a tragedy like Sandy Hook would occur again? Limiting the size of magazines on military-style weapons could reduce the likelihood of another Sandy Hook-like tragedy, which is why I voted for and have now cosponsored Senator Lautenberg’s commonsense bill," said a Casey statement late Tuesday afternoon.
His move to become a co-sponsor illustrates Casey's level of commitment to a cause he long opposed.
"Thank you @SenBobCasey for committing to public safety & co-sponsoring my bill to ban high-capacity ammo magazines," said a post from Lautenberg's Twitter account.
Casey had previously spoken out against new gun laws, even after previous mass shootings at Virginia Tech and in Aurora, Col., but he had a change of heart after the schoolhouse massacre that left 20 children and six educators dead. Casey said he was "haunted" by images from that incident.
He said then he would support proposed bans on assault weapons and high-capacity magazines, and he voted for those measures, along with the expanded background checks proposed by Sens. Pat Toomey (R., Pa.) and Joe Manchin (D., W.Va.) last month, but all three measures fell short.
While many lawmakers, including Toomey, have moved on to other issues since then, Casey has continued to speak out on gun laws, including in several television appearances. 
"There's a lot of frustration and I think that will continue but it should fuel an effort to try this again," Casey said in an April 22 appearance on MSNBC's Morning Joe. Expanded background checks, he said then, would not be "nearly enough" in his view.
The bill limiting magazine sizes is also backed by Connecticut Sen. Richard Blumenthal. He, Lautenberg and Casey are all Democrats.
The plan faces a difficult road to passage in the senate. The proposal got just 46 of the 60 votes needed to clear the senate last month, even with the Newtown shooting still fresh in the public's memory.
With some lawmakers facing an angry backlash for their votes against expanding background checks, some gun control advocates are hopeful that the senate could take another run at passing new gun laws, but it appears that any new votes will have to wait for a significant amount of time, and would most likely be focused on a new version of the Toomey-Manchin background check plan.
A public outcry would likely have to drive any new push.