Washington -- Fire-spitting angry, Sen. Dianne Feinstein told her Senate colleagues to "show some guts" as her ban on assault weapons failed in the Senate on Wednesday in the face of relentless opposition from the National Rifle Association.

The California Democrat was in full fury, spilling a stream of outrage beyond the mere two minutes allowed on her amendment to gun legislation that was crafted in response to the massacre of 20 schoolchildren and six adults in Newtown, Conn., four months ago.

Her California colleague and fellow Democrat, Sen. Barbara Boxer, shouted for order so that Feinstein could be heard in the evening round of votes that left efforts to stem the availability of guns in shreds.

"We have had enough of the development of highly militarized weapons, easy to shoot, big clips, 100-plus bullets in each large-velocity gun, falling into the hands of grievance killers, juveniles, people mentally disturbed," Feinstein said.

"There will be no background checks, apparently," she added, referring to the failure moments earlier of a vote on a bipartisan amendment by two pro-gun conservatives, Pennsylvania Republican Pat Toomey and West Virginia Democrat Joe Manchin, to expand background checks on gun buyers.

That bipartisan amendment was the guts of the gun control effort. It won a 54-vote majority, but failed under the 60-vote demand of the filibuster, drawing four Republicans but losing four Democrats.

Feinstein, who became mayor of San Francisco in 1978 after the assassinations of Mayor George Moscone and Supervisor Harvey Milk, attempted against heavy odds to include in the gun legislation a revamped version of her 1994 assault weapons ban, one of her first and most important achievements in two decades in the Senate.

Filibuster threshold

The 1994 ban passed by one vote on a simple majority. It expired a decade later. Her new version required, like virtually all legislation in the Senate these days, 60 votes, because everything is routinely blocked by filibuster. It didn't come close, failing 40-60 against a solid phalanx of Republicans and a 15-vote contingent of Democrats from gun-friendly rural states.

"We're here on six-year terms for a reason, to take votes on difficult issues," Feinstein said. "Everything needs 60 votes today. This is supposed to be a majority body. We have crafted an assault weapons bill to really represent the people of America. Every single poll has shown support for this."

Warned that her time had expired, Feinstein acknowledged her impending defeat, but excoriated her colleagues.

"I know how this is going to end," Feinstein said. "The despair and the dismay of families standing out there whose safety we need to protect, and we don't do it," she said, as some families of the victims of Newtown and other mass killings watched from the gallery.

President Obama said the defeats of the expanded background checks and assault weapons ban marked a "shameful day for Washington."

Against Feinstein

Sen. Charles Grassley, R-Iowa, stood to rebut Feinstein, saying her amendment would constitute the "largest ban of guns in the history of the republic."

He said studies showed her previous ban did not stop the killer in the 1999 Columbine, Colo., school massacre and would not have stopped the Newtown shooter. Grassley said there is "no evidence" that the Feinstein ban would reduce multiple-victim shootings or wounds per victim.

"Criminals do not care in the least" if military-style weapons are banned, Grassley contended, saying Feinstein's bill would ban weapons based on their cosmetic appearance but leave more powerful weapons untouched.

"This is a slippery slope of compromising the Second Amendment," Grassley said, his voice rising. "You go down that road, you're going to find it easier to compromise other things in the Bill of Rights."

Winning over Reid

So impassioned was Feinstein that she won the vote of Senate Majority Leader Harry Reid, a Nevada Democrat who a month ago told her that her assault weapons ban would be omitted from the gun legislation.

It was a big reversal for rural-state Reid.

"We can and should make the same common-sense approach to safeguard Americans from modern weapons of war, assault weapons," Reid said. "That's why I will vote for Dianne Feinstein's assault weapons ban, because we must strike a better balance between the right to defend ourselves and the right of every child in America to grow up safe from gun violence."

Feinstein said she would not give up her fight to ban assault weapons, certain that in the future, "we will be forced to confront other incidents like Newtown, where innocents are murdered with one of these weapons of war."