Just hours before it was going to expire, Congress approved and President Barack Obama signed a law to extend for ten years a ban on firearms that can pass through metal detectors unnoticed. But Congress rejected a proposal to strengthen the law by including a provision that would have toughened requirements in anticipation of guns manufactured via 3-D printing technology.

It was the first and only federal gun control legislation passed since the Sandy Hook shootings and it appears to have happened with the tacit support of the National Rifle Association. Not-so-coincidentally, the gun lobby is adamantly opposed to any extensions of the law’s provisions.

An NRA-endorsed North Carolina Republican, Rep. Howard Coble, and Rep. Steve Israel, a New York Democrat, were sponsors of the legislation to extend the 25-year-old law that was first signed by President Ronald Reagan in 1988. Israel is also the sponsor of a tougher measure, which did not get approval, that would have required guns to contain unremovable pieces of metal to ensure they would be detectable. But on the House floor he said, “I would have liked to close that loophole. But frankly, I believe even a loophole in a law is better than no law at all.”

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In the Senate, Chuck Schumer, D-N.Y., and Bill Nelson, D-Fla., proposed a requirement that all guns contain unremovable pieces of metal to ensure they would be detectable. Sen. Chuck Grassley, R-Iowa, who has garnered much financial support from the NRA over the years, objected. That’s all it took to grind debate in the Senate to a halt; Democrats, not wanting to allow the ban on undetectable firearms to expire, didn’t press the point. “I am pleased that we are passing this legislation today but we must all remember that this is a bare minimum,” said Sen. Ed Markey, D-Mass.

The NRA was notably quiet during the debate over the legislation in the House, issuing a statement only after the bill passed. And that statement was carefully worded: “The NRA strongly opposes ANY expansion of the Undetectable Firearms Act,” it wrote. “By simply reauthorizing current law, however, [the bill] does not expand the UFA in any way.”

In strong contrast, the National Association for Gun Rights, which bills itself as the no-compromise gun lobby, urged activists to oppose the Coble bill: “[L]et them know that a vote to reauthorize the so-called “undetectable” gun ban is a vote for more gun control and less freedom.”

Meanwhile, gun control groups claimed the new law as a victory: “This week, Congress heard the voices of the majority of Americans who support sensible gun laws, when it passed legislation to extend the Undetectable Firearms Act for another 10 years,” wrote the Brady Campaign to Prevent Gun Violence in a message to activists. The group added that “there is more work to be done to ensure the new technologies, like 3D printed guns, can’t slip through security lines.”

Even so, the effort to expand the undetectable firearms provisions did not spawn the same kind of all-out effort that caused a spike in advertising and lobbying expenditures by gun control groups earlier this year, when Congress was debating background checks and restrictions on assault weapons. A representative of the Brady Campaign to Prevent Gun Violence told Sunlight that the organization has been lobbying for the ban on undetectable weapons during the current quarter. But the Brady Campaign spent $40,000 lobbying Congress in 2012 compared to the NRA’s nearly $3 million. The NRA was one of three guns rights groups to list the proposed expansion of the plastic gun ban on their third quarter lobbying report. The others were Gun Owners of America and the National Association for Gun Rights.

Sam Hoover, staff attorney for the Law Center to Prevent Gun Violence, was direct about his group’s support of the 3-D printing legislation. “We are definitely in favor of the more expansive regulation,” Hoover told Sunlight, adding that his organization is “in support of any legislation restricting firearms that could pass undetected through metal detectors.” But a spokesman for New York City Mayor Michael Bloomberg, a founder and major funder of Mayors Against Illegal Guns — one of the most well-heeled gun control groups — was more measured on the subject of Israel’s legislation. “We thank Congressman Israel for his leadership in working to keep New Yorkers safe,” said John Feinblatt, a Bloomberg advisor. “Gun violence is a national public safety crisis that deserves the urgent attention of our leaders in Washington, and we hope many will follow the congressman’s example.”