Washington - During a lengthy and at times emotionally wrenching news conference, Sen. Dianne Feinstein on Thursday announced legislation that would ban the sale and manufacture of 157 types of semi-automatic weapons, as well as magazines holding more than 10 rounds of ammunition.

The bill, which Feinstein, D-Calif., introduced in the Senate on Thursday afternoon, would exempt firearms used for hunting and would grandfather in certain guns and magazines. The goal of the bill, she said, would be "to dry up the supply of these weapons over time."

Surrounded by victims of gun violence, colleagues in the Senate and House and several law enforcement officials, and standing near pegboards with 10 large guns attached, Feinstein acknowledged the difficulty in pursuing such legislation, even when harnessing the shock and grief over the shooting of 20 schoolchildren in Newtown last month.

"This is really an uphill road," Feinstein said.

Feinstein was joined Thursday by several other lawmakers, including Rep. Carolyn McCarthy, D-N.Y., who will introduce companion legislation in the House, and Sen. Richard Blumenthal, D-Conn., who emotionally recalled the day when the children and adults were gunned down in Newtown. "I will never forget the sight and the sounds of parents that day," he said.

Several gun violence victims, families of those killed and others gave brief statements of support for the bill.

Feinstein's bill - which, unlike the 1994 assault weapons ban, of which she was a chief sponsor, would not expire after being enacted - would also ban certain characteristics of guns that make them more lethal and would require that grandfathered weapons be registered. More than 900 guns would be exempt for hunting and sporting.

Such a measure is opposed by the National Rifle Association and many Republican lawmakers, as well as some Democrats.

Since the expiration of a ban on assault weapons in 2004, there has been a deep reluctance among lawmakers to revisit the issue. They cite both a lack of evidence that the ban was effective and a fear of the gun lobby, which has made significant inroads at both the state and federal level in increasing gun rights over the past decade.

Many lawmakers, including some Democrats, prefer more modest measures to curb gun violence, like a bill that would enhance background checks of gun buyers or focus on enforcement of existing laws.