But some gun experts say the lists of banned and exempted firearms show a lack of understanding and expertise of guns.
"There's no logic to it," said Greg Danas, president of a Massachusetts-based expert witness business and firearms ballistic laboratory. "What kind of effect is it going to have?"
Feinstein's bill defines an assault weapon as a semi-automatic firearm with a detachable magazine that has one of several military characteristics that are specified in her legislation. Examples of those characteristics include a pistol grip, which makes a firearm easier to hold, and a forward grip, which makes the firearm easier to stabilize to improve accuracy. The definition is similar to the one in Congress' original ban on assault weapons, which went into effect in 1994 and was widely criticized for outlawing firearms based on cosmetic features.
Feinstein was behind the 1994 law which, at the time, protected more than 600 firearms. The current bill would exempt by name and model more than 2,200 firearms by name and model.
Feinstein said her staff had worked for more than a year to draft updates for the ban that expired in 2004, and it was apparent in the wake of recent mass shootings that now was the time to introduce a new bill. She said her staff consulted with law enforcement agencies and policy experts for months to create the expanded list.
Naming firearms that would remain legal under an assault weapons ban is a politically motivated gesture that was used to help pass the original ban in the early 1990s, people familiar with the process said.