(CNN) — Almost six weeks after the Connecticut shooting rampage that killed 20 first-graders, Sen. Dianne Feinstein on Thursday will propose a new federal ban on some assault weapons, as well as ammunition magazines that hold more than 10 rounds.
The legislation, which would update a previous assault weapons ban that expired in 2004, is opposed by the nation’s powerful gun lobby, led by the National Rifle Association.
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.
Feinstein, who authored the 1994 Assault Weapons Ban that Congress declined to renew 10 years later, will have examples of weapons that would be banned at Thursday’s news conference, including some currently against the law in the District of Columbia, Democratic sources told CNN.
The California Democrat coordinated with police on displaying illegal weapons, according to the sources. NBC’s David Gregory recently came under investigation for holding a banned ammunition magazine on the network’s “Meet the Press” program broadcast from Washington.
President Barack Obama called for renewing the assault weapons ban as part of his package of gun control proposals announced earlier this month in response to the December 14 Newtown school massacre and overall gun violence in America.
Feinstein’s measure would stop the sale, transfer, importation and manufacturing of more than 100 specialty firearms and certain semi-automatic rifles, as well as limiting magazines to 10 rounds or less, according to her website. Not all of the weapons in the bill meet the technical definition of assault weapons.
The measure would not cover weapons already owned before it passed, as well as other hunting, sporting, antique, manually operated and disabled weapons, the website said.
Those exemptions were an apparent effort to garner support for the measure from conservative Democrats and others expected to face fierce lobbying by the NRA and constituents.
Supporters of more gun control acknowledge the constitutional right to bear arms, but argue that rifles capable of firing multiple rounds automatically or semi-automatically exceed the reasonable needs of hunters and other gun enthusiasts.
They also contend that high-capacity ammunition magazines provide the capability for mass shootings such as the Newtown massacre.
Opponents contend the Second Amendment forbids the government from this type of limit on weapon ownership by citizens. They worry that such a weakening of gun rights would signal a shift that would leave citizens defenseless against criminals and, some also argue, against potential future government tyranny or abuse. Instead, the NRA has called for increasing armed guards at schools to protect students.
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.
Vice President Joe Biden led a panel assembled by Obama 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.
According to the survey, 55% of Americans generally favor stricter gun control laws, with 56% saying that it’s currently too easy to buy guns in this country. However, only 39% say that stricter gun controls would reduce gun violence all by themselves.
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.
A senior administration official told reporters the price tag for the entire package was $500 million.
A main focus of Obama’s steps is closing loopholes in background checks. Across the country, more than a million people failed background checks to buy guns during the past 14 years because of criminal records, drug use or mental health issues, according to FBI figures.
That figure, however, is a small fraction of overall gun sales.
Obama also called for more money to strengthen gun safety at schools, including hiring more counselors such as retired law enforcement officers to help educate students on gun issues. He also called for more funding for communities to hire more police officers, but stopped short of seeking the NRA’s proposal for armed guards at every school.
The CNN/Time/ORC poll showed that respondents favored armed guards in schools, 54% to 45%.
In New York, Democratic Gov. Andrew Cuomo recently signed into law a series of new gun regulations, the nation’s first since the Newtown shootings.
The measures, which won approval from the state legislature, include a statewide gun registry and add a uniform licensing standard across the state, altering the current system, in which each county or municipality sets a standard.
Residents also are restricted to purchasing ammunition magazines that carry seven bullets, rather than 10.
Lawmakers in at least 10 other states are reviewing some form of new gun regulations.
By Dana Bash and Tom Cohen
CNN’s Halimah Abdullah contributed to this report.
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