Last-minute efforts to close a loophole allowing guns made on 3D printers to escape airport metal detectors are expected to be blocked by Republicans in the Senate on Monday evening.
This latest setback to gun control efforts in Congress comes just days before the first anniversary of the Newtown elementary school shooting, which campaigners had hoped would encourage far wider reform including background checks and an assault weapons ban.
Instead, even minor tweaks to existing gun control legislation are failing to make progress in either the House of Representatives or Senate, and reauthorisation of current rules is far from guaranteed.
Senators will vote at 6pm on a bill to extend the Undetectable Firearms Act, a Reagan-era bill that prohibits the sale or use of guns made entirely from plastic due to the risk that they can be carried unnoticed through metal detectors.
The current bill expires on December 9 and was hurriedly extended by the House last week in a thinly attended voice vote.
However campaigners say it is inadequately drafted to cope with the proliferation in plastic weapons made possible by recent advances in 3D home printing technology.
In particular, the bill does not stipulate whether metal parts required under the law can be removed without hampering the functioning of the weapon.
Instead, Democrats are attempting to introduce an updated version requiring metal parts to be integral and impossible to remove.
New York senator Chuck Schumer will attempt to beat today's deadline for extending the law by seeking so-called unanimous consent to vote on the enhanced measure at the same time as the original reauthorisation.
But Republican opponents led by senator Chuck Grassley of Iowa are thought likely to block the attempt on the grounds that the two bills should be debated separately.
An earlier bill introduced by congressman Steve Israel is also stalled in the House and unlikely to be given floor time by House speaker John Boehner.
Republicans have opposed most gun control measures attempted in recent years, although a small number of GOP senators crossed the aisle to support enhanced background checks.
Increased rancour in the Senate is also frustrating attempts to seek bipartisan consensus as Republicans are increasingly unwilling to co-operate with a Democratic leadership they accuse of abusing the rights of the minority party.
Democrats will attempt on Monday the first use of new rules designed to circumvent the filibustering of judicial nominees, voting to ratify a controversial Obama appointment for the Washington circuit appeal court: Patricia Millet.
What little bipartisan goodwill remains is largely concentrated onfinalising a budget deal before Friday's deadline for avoiding another government shutdown.
The chief negotiators – Democratic senator Patty Murray and representative Paul Ryan – are thought to be close to a deal that would set a new two-year federal budget of around $1tn.
However they are not expected to have found enough common ground to address wider tax and revenue issues needed to reduce the deficit, and are aiming at only limited relief from the so-called sequester cuts – introduced after the collapse of earlier negotiations.