The US has have moved to boost funding of the national background check system for firearm sales, a small but symbolic step toward broader gun law reform following recent mass shootings.
The measure provides $US19.5 million ($A21.10 million) in additional grant financing to help states submit records to a federal database aimed at preventing felons and the mentally ill from buying weapons.
Supporters of the amendment, which passed 260 to 145 as part of a $US51 billion spending bill for the Commerce and Justice Departments expected to be approved later on Thursday, say the measure would keep guns out of the hands of potentially dangerous people.
The issue was brought into shocking focus last weekend when a deranged student went on a rampage near the University of California at Santa Barbara, fatally stabbing and shooting six people before killing himself.
Police said the suspect purchased his guns legally, reportedly despite years of psychological therapy.
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"Our national criminal background check system is only as good as the data you put in it, and right now all the information isn't getting into the system," the bill's sponsors, led by House Democrat Mike Thompson, said in a statement immediately after the vote.
"When this happens, we can't enforce the law, and criminals, domestic abusers, or dangerously mentally ill individuals who otherwise wouldn't pass a background check can slip through the cracks and buy guns."
Such holes in the system in 2007 allowed a 23-year-old Virginia Tech student to purchase guns, which he used to kill 32 people in one of the deadliest mass shootings in US history.
Two years earlier, a judge had declared the man mentally ill, but Virginia authorities did not report the finding to the NICS system, and he was able to pass a background check.
The House measure would raise funding to a total $US78 million for fiscal year 2015 for the National Instant Criminal Background Check System (NICS), the FBI database that has prevented more than 1.5 million felons, domestic abusers and fugitives from buying guns since it was created by Congress in 1993.
States have been slow to get more disqualifying records into the system, which is largely voluntary.
Thompson and sponsors including Republican Peter King told colleagues in a letter that 12 states have submitted fewer than 100 mental health records.
The bill is backed by several gun-control groups including Sandy Hook Promise, formed in the aftermath of a 2012 shooting at a Connecticut elementary school that left 26 people dead.
In the wake of that tragedy, President Barack Obama and his Democrats called for bills expanding background checks to include sales on the internet and at gun shows, and banning assault weapons and high-capacity magazines.
The legislation failed last year, handing a victory to pro-gun rights groups like the powerful National Rifle Association.
