http://www.nytimes.com/2013/11/29/u...?nl=todaysheadlines&emc=edit_th_20131129&_r=0 WASHINGTON In the movie In the Line of Fire, a deranged killer smuggles a homemade gun past the Secret Service and tries, unsuccessfully, to shoot the president. That situation might have seemed far-fetched when the film, which starred Clint Eastwood as the agent who dives in front of the assassins bullet, came out in 1993. But today, police officials and members of Congress fear that if a law known as the Undetectable Firearms Act is not renewed and updated when it expires on Dec. 9, firearms that can slip past metal detectors and X-ray machines will become a law enforcement problem across the country. It is not an idle concern: Homemade plastic guns are a reality, made possible by the proliferation of 3-D printing technology that was only getting started when the law was first passed by Congress and signed by President Ronald Reagan in 1988. They are so frightening because they render most standard detection useless, said Tim Murphy, a former deputy director of the F.B.I. The expiring law bans guns that can pass unnoticed through a metal detector, and has been renewed twice in the 25 years since it was first enacted. But with the expiration date a little more than a week away, reauthorizing it has been caught up in a political standoff that has thwarted other recent attempts to enact gun safety legislation. Were on the clock, and as we know, this Congress doesnt deal well with deadlines, said Dan Gross, president of the Brady Campaign to Prevent Gun Violence. For now, the extension is delayed as lawmakers fight over whether to simply extend the law or amend it to include new provisions aimed specifically at 3-D printed weapons. Shortly before the Senate broke for its Thanksgiving recess, it set aside a measure to extend the law for a year because of objections by Republicans. Senator Jeff Sessions, Republican of Alabama, said he was concerned not about extending the law as written but about senators who support gun safety measures using the law as a backdoor way of attaching more provisions when it expires again. Theyre considering altering it, putting more language in it, Mr. Sessions said. Theres concern that it may be altered in a way that would be problematic. The House is expected to approve a 10-year extension of the law when it returns next week. Democrats, led by Representative Steve Israel of New York, want to include the 3-D-printed weapons provision, but Republicans have agreed only to consider renewing the law as it is now. Its hard to believe that anyone would oppose a piece of legislation like this, so tied into, so connected with our safety, said Senator Charles E. Schumer, Democrat of New York, one of the senators leading the effort to extend the law. In a world of terrorism, to say that we would make legal guns that can pass through metal detectors so people can slip them through airports, stadiums, schools? The National Rifle Association, whose position will carry significant weight with many in Congress, has not publicly signaled where it stands. A spokesman for the N.R.A. did not respond to several requests for comment. But Gun Owners of America, a smaller and more vocal gun rights group, said that both the extension of the current law and the new provisions would be unnecessary because 3-D printing technology was still so new and not widely available. Theyre not going to be in Kinkos, said Larry Pratt, the groups executive director. And at the moment, they cant fire that many rounds. Its just not something that were going to be dealing with anytime soon. Those who argue that these guns are not a true safety threat often point to the cost of 3-D printers, which can be as expensive as some automobiles. But as the technology becomes less expensive and accessible, concern is growing. To technically comply with the current law, manufacturers of 3-D-printed guns only have to make their firearms detectable to security screeners in some way, usually by including some form of metal, which can be nonfunctional and easily removable. The Bureau of Alcohol, Tobacco, Firearms and Explosives recently assembled one such gun using designs downloaded from Defense Distributed, a group based in Texas that describes itself as dedicated to defending the civil liberty of popular access to arms as guaranteed by the United States Constitution. The bureau tested the gun and found it capable of firing multiple .380-caliber metal bullets. Federal authorities demanded the group remove the designs from its website. To close the loophole in the current law, the changes proposed by Democrats would require that an essential, nondetachable piece of the gun be made of enough metal to be picked up in a security screening. But some officials say the real challenge is to find a way to detect plastic weapons, and want more money devoted to that. The law is not the story someone that wants to do harm is not going to abide by the law, said Mr. Murphy, the former F.B.I. official. It may stop large-scale production, but wont stop the lone wolf or adversary. Someone needs to be thinking bigger. After attempts by terrorists to bring down airliners over the past decade, the government and security companies made some strides in detecting plastic explosives. But far less time and money were devoted to detecting plastic weapons, because they were not seen as a major threat. While body scanners are considered a reliable way to detect a weapon on a persons body, they are expensive and difficult to transport and have raised concerns about privacy. Theyre so good they can see a credit card in your pocket, said a senior law enforcement official who has overseen the use of such machines. But people dont like them. And people dont like pat-downs.