Nightly News | November 17, 2013
>>> there is new concern tonight among the country's police that it's becoming much easier to make lethal plastic guns that could be slipped past metal detectors just as an important protection against those weapons is about to be lost. we get more on that story from nbc's justice correspondent pete williams .
>> reporter: this is what has law enforcement organizations so worried, a plastic gun that can withstand firing several bullets but cannot be discovered by metal9/ detectors in public buildings, schools, sports arenas and airports.
>> this would be really dangerous for travelers, it would mean a terrorist, criminal, mentally ill person could walk through a metal detector undetected, completely undetected and perfectly legal.
>> reporter: the gun is made using machines called 3-d printers widely available that layer down thin layers of plastic to build objects. computer instructions for this version called the liberator are circulating on the internet developed by a group in texas headed by cody wilson, a law student who opposes government regulations.
>> we should have the right to pursue creative endeavors and pursue anything we want.
>> reporter: his design calls for putting a four ounce chunk of steel into the gun so it can be discovered by hand held or walk-through metal detector , even so the metal piece can easily be removed, making the gun undetectable and illegal to possess but the federal law that bans undetectable firearms is about to expire.
>> it is a matter of common sense and common security to extend the undetectable act and modernize it.
>> you could manufacture this in about a day and a half.
>> reporter: officials at say plastic guns can be made with cheaper 3-d printers. this atf) exploding the first time they're fired even though they were made according to instructions on the internet with various guns and parts.
>> there really is no hunting or sporting/7y purposeses for a plastic weapon that can blow up in your hands or hurt the collector of sportsmen around you.
>> reporter: now the atf and others in law enforcement who worry about plastic acts hope congress acts before the law expires december 10th . pete williams , nbc news washington.