Almost six weeks after the Connecticut shooting rampage that killed 20 first graders, Feinstein said she planned to introduce her measure later Thursday, with Reps. Carolyn McCarthy of New York and Ed Perlmutter of Colorado doing the same in the House.
Feinstein's proposal would upgrade an assault weapons ban that expired in 2004 and also outlaw ammunition magazines that hold more than 10 rounds.
She said the goal is to "dry up the supply of these weapons over time."
"These massacres don't seem to stop," the California Democrat lamented, listing notorious rampages of past years known by the lone name of their locations -- Columbine, Virginia Tech, Aurora, Tucson and Oak Creek.
"We should be outraged at how easy it is" for attackers to get hold of the semi-automatic weapons or large-capacity magazines used in those slaughters, Feinstein told the event at the U.S. Capitol that she organized.
Her legislation is opposed by the nation's powerful gun lobby, led by the National Rifle Association. That means that despite a push by the White House and Democrats for tougher gun control steps, Feinstein's full measure is given little chance of winning congressional approval.
In a statement on Thursday, the NRA said that Feinstein "has been trying to ban guns from law-abiding citizens for decades."
"The American people know gun bans do not work and we are confident Congress will reject Senator Feinstein's wrong-headed approach," the organization added.
In a sign of the gun lobby's influence, a nine-day sports and outdoor show scheduled to take place in Pennsylvania next month was postponed Thursday because the NRA withdrew its support over the decision by organizers to ban the display of "modern sporting rifles" -- the kind of semi-automatic weapons targeted by Feinstein's proposal.
At her Washington event, Feinstein acknowledged that enacting a ban was "really an uphill road," adding: "If anyone asks if we can win this, the answer is we don't know, because it's really uphill."
She then made a plea for people to call their senators and House members to declare "enough is enough," adding that a mobilized public is "stronger than the gun lobby."
Later Thursday, Vice President Joe Biden made a similar appeal in an online discussion on Google, saying: "Make your voices heard."