An attempt to update firearms rules to cover weapons made using 3D printers was blocked on Monday night as a fresh row over gun control erupted in the Senate.
Existing legislation requires all plastic weapons made or carried in the US contain some metal parts so they can be picked up by security detectors.
The law, dating back to the 1980s, was due to expire on December 9 but was extended by both the House and Senate with only hours to spare.
Democrats, led by New York senator Chuck Schumer, also attempted to introduce an amendment to close a loophole that they claimed will become a growing security risk now that individuals can produce homemade plastic weapons using 3D printers.
Their amendment sought to criminalise designs that include metal pins that can be temporarily removed to evade security checks in airports and other sensitive locations.
Instead it would have required all plastic weapons to include metal parts that are integral to the design and cannot be removed without compromising the gun.
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