A bill introduced last month by Sen. Dianne Feinstein, D-Calif. would ban 157 specific firearms designed for military and law enforcement use and exempt others made for hunting purposes. It also would ban ammunition magazines that hold more than 10 rounds.
Yet there are firearms that would be protected under Feinstein's proposal that can take large capacity magazines like the ones used in mass shootings that enable a gunman to fire dozens of rounds of ammunition without reloading.
Feinstein said in a written response to questions from The Associated Press that the list of more than 2,200 exempted firearms was designed to "make crystal clear" that the bill would not affect hunting and sporting weapons.
The December shooting at an elementary school in Newtown, Conn., that left 26 students and educators dead forced Washington to focus on curbing gun violence, a risky political move not tried in decades.
The gun industry, which is fighting any sort of ban, says gun ownership in the U.S. is the highest it's ever been, with more than 100 million firearms owners.
Obama and Vice President Joseph Biden have traveled around the country in an effort to gain support for new laws. Feinstein's proposal is the only sweeping piece of legislation designed to ban assault weapons currently being considered.