The US Senate has approved a 10-year extension of a ban on plastic guns invisible to metal detectors but has rejected tougher restrictions called for by gun-control advocates.
The bill was approved by a Senate voice vote one week after it passed the House of Representatives.
Democrats had aimed to require a gun's firing mechanism to contain at least one undetachable metal piece.
The ban has gained new relevance with the spread of at-home 3D printing.
The proposed 10-year extension of the Undetectable Firearms Act now goes to President Barack Obama for his approval.
Without further Congressional action, the 25-year-old law was scheduled to expire on Monday.
Senate Republicans failed to approve what Democratic Senator Chris Murphy described as a "common-sense" provision requiring plastic guns to contain a detectable metal component.
"If anybody in the Senate is so concerned about what they consider to be loopholes in the law, this obviously should have been done through hearings and the introduction of legislation long ago," Republican Senator Charles Grassley subsequently told the media of the Democrat-led provision.
The National Rifle Association (NRA), America's largest and most powerful gun lobby group, had issued a statement prior to the House vote on 3 December opposing any expansion of the law.
Analysts had previously said the NRA's lobbying power left it unlikely the law would be broadened before next year's mid-term election.