The Colorado Court of Appeals, in a unanimous opinion issued Thursday, upheld the state’s ban on large-capacity ammunition magazines of 15 rounds or more.

The lawsuit dates back to the contentious 2013 state legislative session in which Democrats, who controlled both the House and Senate, passed a trio of gun-control laws, including one that banned sales or transfers of an ammunition magazine holding 15 rounds or more. Magazines purchased prior to the law’s passage were grandfathered in, meaning the owner didn’t have to dispose of it.

The case was brought by Rocky Mountain Gun Owners (RMGO), a Loveland-based gun-rights advocacy group. Several other groups also signed on with the plaintiffs, including the Colorado Law Enforcement Firearms Instructors Association; sheriffs Chad Day of Yuma County, Shannon K. Byerly of Custer County, Steve Reams of Weld County and Sam Zordel of Prowers County; and the Independence Institute, a Denver libertarian think tank.

The appeals court concluded that the logic for passing a ban on large-capacity magazines was based on a “legitimate governmental interest in public health and safety.” In their opinion, the justices pointed out that there have been 27 mass shootings in Colorado that used large-capacity magazines between 1999 and 2016. That contrasts with 11 mass shootings involving large-capacity magazines in the period between 1967 and 1998, the opinion noted.

Colorado’s ability to regulate guns centers around a 1994 case, Robertson v. City of Denver. In that case, the Colorado Supreme Court decided “the state may regulate the exercise of [the right to bear arms] under its inherent police power so long as the exercise of that power is reasonable.”

The legislature’s intent in passing the 2013 law was a “legitimate governmental purposes of reducing deaths from mass shootings,” the opinion stated. And while the plaintiffs argued that the 2013 law hasn’t made a dent in overall gun violence or deaths from guns, the appeals court said that “legislation need not solve all gun problems to be constitutional. … We conclude that the statutes burden only a person’s opportunity to use [a large-capacity magazine], not a person’s right to bear arms in self-defense.”

RMGO’s appeal came after the Denver District Court ruled against the original case. The lower court found that the plaintiffs’ claim that the statutes make “almost all magazines and semiautomatic weapons illegal” turned on an unreasonable reading of the statutory definition of a large-capacity magazine.

The RMGO appeal of the District Court’s ruling centered on two arguments: That magazine ban should “be subject to a heightened standard of review” and that the statute was unconstitutional because it would ban “an overwhelming majority of magazines.”

The appeals court disagreed with both assertions, stating even if they considered the statutory law “ambiguous, the legislative purpose is to reduce the number of people who are killed or shot in mass shootings, not to ban all gun magazines,” the opinion stated. Further, the statute does not prevent Coloradans from exercising their constitutional right of self-defense, the opinion indicated.

The plaintiffs didn’t assert that the 2013 law violated their 2nd Amendment rights under the U.S. Constitution, only their rights under the state constitution. According to Christopher Jackson, an attorney who has worked on previous lawsuits involving guns but is not involved in the current case, there’s a big difference. Colorado’s constitutional provisions on firearms include language not found in the U.S. Constitution. The state document states that a person has a right to “keep and bear arms in defense of his home, person and property, or in aid of the civil power when thereto legally summoned.”

The plaintiffs can appeal to the state Supreme Court, and seek for a standard of review different than the one created by the Robertson case, Jackson said.

Dudley Brown, executive director of RMGO, told Colorado Politics the group will appeal Thursday’s ruling, which he said was not unexpected.

“From day one we knew this was a long haul through the courts, made more difficult by a Republican attorney general [Cynthia Coffman] who clearly wants to keep this magazine ban on Colorado’s books,” Brown said.