The Trump administration has opened a new legal front in America’s gun-rights battle, filing suit against Colorado over its long-standing restriction on firearm magazines capable of holding more than 15 rounds.
The challenge, launched by the U.S. Department of Justice, seeks to dismantle a law Colorado enacted in 2013 after the mass shooting inside an Aurora movie theater that left 12 people dead and dozens wounded. Federal officials now argue the measure violates constitutional protections guaranteed under the Second Amendment.
At the center of the dispute is a familiar question that continues to divide courts, lawmakers and gun owners alike: whether limits on ammunition capacity are a reasonable public-safety safeguard or an unconstitutional curb on commonly owned firearms.
The DOJ’s complaint argues that magazines exceeding 15 rounds are not niche accessories but standard components bundled with many of the country’s most widely purchased semi-automatic rifles and pistols, including AR-15-style firearms. Because tens of millions of Americans legally possess such weapons, the administration contends the state cannot prohibit equipment considered “in common use.”
The lawsuit leans heavily on the Supreme Court’s landmark 2008 ruling in District of Columbia v. Heller, which affirmed an individual’s right to possess firearms for lawful purposes such as self-defense. According to the federal government, Colorado’s ban effectively blocks access to ordinary firearm configurations commonly sold across the United States.
Colorado officials pushed back immediately.
State Attorney General Phil Weiser defended the law as a legitimate safety measure designed to reduce the devastation caused during mass shootings. He accused the Justice Department of distorting the role of its civil rights division and maintained that magazine restrictions are compatible with constitutional protections.
Supporters of the law say limiting ammunition capacity can create critical pauses during attacks, giving victims an opportunity to escape or intervene while shooters reload. Gun-control advocates often point to research suggesting shootings involving high-capacity magazines result in significantly higher casualty counts.
This is not the first legal assault on Colorado’s restrictions. A previous challenge brought years ago by sheriffs, gun dealers and shooting-range operators collapsed in federal appeals court after judges ruled the plaintiffs lacked standing to sue because they failed to show direct personal harm.
The new federal case arrives amid a broader campaign by the Trump administration against state and local firearm regulations. Just a day earlier, the Justice Department filed another lawsuit targeting Denver’s ordinance restricting certain semi-automatic rifles classified as assault weapons.
Colorado is among a smaller group of states that specifically cap magazine capacity. Across the country, fourteen states and Washington, D.C., maintain similar restrictions, though most impose a stricter 10-round ceiling. Colorado’s limit stands at 15 rounds, while Delaware permits up to 17.
The latest lawsuit now places Colorado squarely in the middle of another major constitutional showdown over the boundaries of gun regulation in post-Heller America.
