A federal judge in Denver refused Wednesday to block a new Colorado state law that limits the size of ammunition magazines.
Judge Marcia Krieger said she could not issue an injunction because the law already is in effect.
"It is already the law of the state and there is nothing for me to enjoin," Krieger said.
Krieger disclosed her decision at a hearing on a lawsuit by Colorado sheriffs who are challenging the law that went into effect July 1.
The law, passed in the wake of mass shootings in Colorado and Connecticut, bans magazines that hold more than 15 rounds. The sheriffs contend it violates the Second Amendment right to keep and bear arms and also is too vague to enforce.
The law was a major victory for Colorado Democrats, who rallied majorities in the House and Senate this spring to pass it without Republican support. Democrats also expanded background checks to include online and private firearm sales.
Sheriffs in 54 of Colorado's 64 counties filed the lawsuit in May seeking to overturn both laws. Most of the sheriffs behind the lawsuit represent rural, gun-friendly parts of the state.
Krieger also said Wednesday she had been told that the plaintiffs and the governor's office reached an agreement late Tuesday on how to enforce the law while the legal challenge proceeds. Details on that agreement weren't immediately released.
The lawsuit contends the magazine law lacks clarity because it bans magazines that are "designed to be readily converted" to hold more than 15 rounds.
The Colorado attorney general's office, which is defending the state, had previously issued guidance to law enforcement on how the limit should be enforced, saying magazines that hold 15 rounds or fewer can't be defined as "large capacity" simply because they can be modified to include more.
Opponents maintain that many magazines can be easily converted to hold more rounds. David Kopel, the attorney representing the sheriffs, said he also was arguing that the law is vague about what happens to larger magazines that were grandfathered in.
The sheriffs decided not to pursue a preliminary injunction for the expanded background checks, given the complexity of the new law and limited time at Wednesday's hearing. Kopel said it's more appropriate to address the background checks at trial.
Democrats argue both laws will improve public safety and are an appropriate response to the massacres at a suburban Denver movie theater last July and at Sandy Hook Elementary School in Newtown, Conn., in December.
Two Democrats — Senate President John Morse and Sen. Angela Giron — face potential recall elections because they supported the laws.
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