Firearm restrictions pitched by Colorado Democrats advanced Monday, as the battle over them intensified with hundreds of gun rights supporters cramming the state Capitol and circling the building all day with car horns blaring. Inside, the husband of former U.S. Rep. Gabrielle Giffords urged lawmakers to pass universal background checks and victims of mass shootings in Connecticut and a suburban Denver movie theater pleaded for more gun controls.

Colorado has become a focus point in the national debate over what new laws, if any, are needed to prevent gun violence in the wake of recent mass shootings, including an attack at a suburban Denver movie theater last summer -- a massacre that brought to mind the Columbine High School shooting of 1999 for many in the state and across the nation.

Lawmakers in the politically moderate state are considering a package of gun control measures, including plans that would limit ammunition magazines to 15 rounds and expand background checks to include private sales and online purchases. Both measures cleared Democratic-controlled committees on 3-2 party-line votes but still need approval from the full Senate, which could debate the bills as soon as this week.

Retired astronaut and Navy captain Mark Kelly told lawmakers that he and his wife support the Second Amendment, but he said the right to bear arms shouldn't extend to criminals and the mentally ill.

Kelly compared the different background check requirements for private and retail sales to having two different lines at the airport, one with security and one without.

"Which one do you think the terrorist is going to choose?" he asked.

Giffords, a former Democratic congresswoman from Tucson, Ariz., was severely wounded in a mass shooting in January 2011 while meeting with constituents.

Gun control opponents say the proposals will not reduce violence. They say lawmakers should focus on strengthening access to mental health services for people who could be dangerous to communities.

The bill hearings were at times testy, and included some outbursts from the audience. After one bill passed, someone leaving the committee yelled "That sucks!" to lawmakers.

"I've never seen such unprofessional behavior," Democratic Sen. Irene Aguilar told the audience at one point.

Meanwhile, gun rights advocates complained that lawmakers limited testimony time and many didn't have a chance to speak on proposals.

The commotion at the Capitol underscored the attention the debate has generated nationally from gun rights groups, such as the National Rifle Association, to victims' families and White House officials.

Several bills before state senators already have cleared the House. And because Democrats control both chambers of the state Legislature, some of the proposals have a strong chance of passing.

Other measures that picked up initial Senate approval would place new restrictions on gun ownership by people convicted in domestic violence cases, and another requires gun buyers to pay for their own background checks.

The state's Democratic governor, John Hickenlooper, supports magazine limits and expanded background checks. He hasn't indicated where he stands on other measures, including whether he supports a proposal that would hold sellers and owners of assault weapons liable for shootings by such firearms.

Gun rights supporters walked the Capitol halls wearing stickers that read, "I Vote Pro-Gun." Several dozen people outside the Capitol waved American flags as light snow fell, and a small plane flew overhead carrying a banner with a message for the governor, "HICK: DO NOT TAKE OUR GUNS!"

One of the nation's largest producers of ammunition magazines, Colorado-based Magpul, has threatened to leave the state if lawmakers restrict the size of its products. Its founder said smaller magazines can be easily connected to each other and the company fears it would legally liable if people were to do that.

About 20 Colorado sheriffs opposed the expanded background checks and the magazine limits. Standing shoulder-to-shoulder in front of lawmakers in committee, they said that both bills were unenforceable.

"This bill just doesn't make any sense from our perspective," Pueblo Sheriff Kirk Taylor said about the bill to limit magazine sizes.

Victims who have lost relatives to gun violence say it's time for legislators to take action.

Tom Sullivan, whose son Alex was among the 12 killed in the Aurora, Colo., theater shooting, was among the people urging lawmakers to pass magazine restrictions.

"He was enjoying the movie one second, and then the next second he was dead," Tom Sullivan said.

Jane Dougherty, whose sister, Mary Sherlach, was a psychologist killed in the shooting rampage at Sandy Hook Elementary School in Newtown, Conn., has been lobbying Colorado lawmakers to pass new gun laws. She said she doesn't understand gun owners who worry the bills are putting a burden on their rights.

She said the Connecticut shooter used "the same type of weapon that we use in war" to "slaughter these babies" and asked lawmakers for stricter gun laws.

"We cannot wait for yet another massacre to transpire," Dougherty said.