Speakers at the event organized by Feinstein rejected arguments that anyone beyond the military or law enforcement officers needed such firepower.
"How are you going to hunting with something like that?" asked Philadelphia Police Commissioner Charles Ramsey, pointing to the assault weapons displayed to his left. "You kill something, there's nothing left to eat."
Continuing bloodshed on the nation's streets -- with dozens dying every day from gun violence -- should be enough evidence to overcome the past inability to get gun control legislation enacted, he argued.
"If the slaughter of 20 babies does not capture and hold your attention, then I give up because I don't know what else will," Ramsey continued, thrusting a pointed finger for emphasis.
At Feinstein's request, people who were injured or lost loved ones to gun violence, including several from the Virginia Tech massacre, then offered their support for her efforts.
Some told of losing a parent or child. Others described how attackers inflicted carnage so quickly.
Pam Simon, a staff member to Rep. Gabrielle Giffords of Arizona, said she was a few feet away from the congresswoman on the day both were shot outside a Tucson grocery store.
"On that day, 30 bullets were delivered in less than 30 seconds," Simon said.
Some of the weapons on display Thursday are currently against the law in the District of Columbia, and Democratic sources told CNN that Feinstein coordinated with police on being able to have the guns there.
NBC's David Gregory was recently investigated for holding a banned ammunition magazine on the network's "Meet the Press" program broadcast from Washington. No charges were brought in that case.
Obama's proposals include expanding and strengthening background checks on gun buyers to ensure all sales include screening to prevent weapons from going to criminals and the mentally ill.
While the gun lobby has indicated support for some improvements in background checks, it remains opposed to other steps, saying they won't prevent criminals from getting weapons.
Instead, gun advocates urge tougher enforcement of existing laws and making criminals serve their full sentences.
Biden led a panel assembled by Obama in December to examine gun control steps after the Newtown shootings, which sparked a fierce public debate over how to prevent such mass killings. Biden's recommendations formed the basis of the package of proposals Obama announced this month.
A recent CNN/Time Magazine/ORC International poll indicated that Americans generally favor stricter gun control, but they don't believe that stricter gun laws alone would reduce gun violence.
In announcing his gun control package, Obama also signed executive actions that call for tougher enforcement of existing laws and require federal agencies to provide data for background checks.
New York state recently enacted a series of new gun regulations, the nation's first since the Newtown shootings. Ten other states are reviewing some form of related action.
The issue is among the most politically divisive in the country, as demonstrated by the decision by Reed Exhibitions to postpone the nine-day Eastern Sport and Outdoor Show scheduled to start February 2 in Harrisburg.
On Tuesday, the NRA withdrew its support for the show due to the decision by organizers to ban modern sporting rifles from exhibition.
"We had called on Reed Exhibitions to reconsider their decision; unfortunately they have steadfastly refused to do so," an NRA statement said. "As a result, the NRA will not be participating in the upcoming show in Harrisburg or in any other shows hosted by Reed Exhibitions that maintain this policy."
In announcing Thursday that the show was off, a Reed Exhibitions official said the intent of excluding "certain products" was to focus on hunting and fishing traditions of the event.
"It has become very clear to us after speaking with our customers that the event could not be held because the atmosphere of this year's show would not be conducive to an event that is designed to provide family enjoyment," said Chet Burchett, the company's president for the Americas.
"It is unfortunate that in the current emotionally charged atmosphere this celebratory event has become overshadowed by a decision that directly affected a small percentage of more than 1,000 exhibits showcasing products and services for those interested in hunting and fishing," he added.