WASHINGTON -- Philadelphia Mayor Michael Nutter and Police Commissioner Charles Ramsey joined some of the Senate’s leading Democrats and several shooting victims today to unveil a new bill to ban assault weapons.

Nutter, speaking to a packed room in a Senate office building, told a story about how, months into his term as mayor, an assailant using an AK-47 killed a Philadelphia police officer.

“Tell his wife, Michelle, and their children why any civilian needs one of those weapons to be out on the streets of our cities,” Nutter said. “This death and destruction must end right now.”

Nutter and Ramsey were part of a press conference led by Sen. Dianne Feinsten, of California, and the Senate’s number second and third ranking Democrats, Illinois’ Dick Durbin and New York’s Charles Schumer.

Alongside the lawmakers were two boards holding an array of military-style weapons that they said would be banned by the proposed new law.

“I don’t think people really understand the firepower that’s out there on the streets that our officers have to face every day and citizens of our cities have to face every day,” Ramsey said. “We’re not trying to seize everybody’s gun but we need reasonable gun control in this country or guess what? It will happen again.”

The bill faces a steep climb to becoming law. Of the major proposals to tighten gun laws, banning assault weapons faces the most opposition in Congress. Plans to improve background checks appear to have the most support. A bill to ban high-capacity clips – those holding 10 bullets or more – seems to fall somewhere in between in terms of political feasibility.

The National Rifle Association has vowed a fierce fight against the laws, saying they are infringements on second amendment rights. Many advocates for gun rights argue that these laws would be the first step toward even farther reaching measures to take away firearms.

New Jersey Sens. Frank Lautenberg and Bob Menendez, both Democrats, are co-sponsors on the assault weapons ban, and Pennsylvania Democrat Bob Casey has said he would support the bill.

Sen. Pat Toomey, a Pennsylvania Republican, has not taken a formal position on the assault weapons bill but people who have met with him say he is unlikely to support the idea.

The bill introduced Thursday bans all semiautomatic rifles and pistols that can accept a detachable magazine and have at least one military feature, as well as semiautomatic rifles and handguns that have a fixed magazine that can hold more than 10 rounds. Other features are also banned. There are 157 specifically-named guns that would be banned by the law, though weapons already lawfully owned would not be affected.

The bill specifically excludes 2,258 hunting a sporting rifles and shotguns.

Unlike the previous assault weapons ban, which ended after 10 years, this bill has no sunset clause.