DENVER (AP) — Colorado sheriffs trying to stop new state ammunition magazine limits go before a federal judge Wednesday to argue that the law, passed in the wake of mass shootings, is too vague to enforce.

The law bans magazines that hold more than 15 rounds and was a major victory for Colorado Democrats, who used 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 a lawsuit in May seeking to overturn both laws, arguing that they violate the Second Amendment right to keep and bear arms. But it's the magazine limit that will be under scrutiny when U.S. District Judge Marcia Krieger hears arguments on whether to grant a preliminary injunction on the law while the lawsuit advances. A written ruling will be issued later.

Both laws took effect July 1. Most of the sheriffs behind the lawsuit represent rural, gun-friendly parts of the state.

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.

"Nobody really knows what that means," said David Kopel, the attorney representing the sheriffs. Opponents maintain that many magazines can be easily converted to hold more rounds. Kopel will also argue 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.

"In the context of something that size, how much can we show in this stage in this case?" Kopel said. He said it's more appropriate to address issues surrounding background checks at trial.

The Colorado Attorney General's office, which is defending the state, has previously issued guidance to law enforcement on how the magazine limit should be enforced, saying that magazines that hold 15 rounds or fewer can't be defined as "large capacity" simply because they can be modified to include more.

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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.

Fallout from the debate continues. Two Democrats — Senate President John Morse and Sen. Angela Giron — face potential recall elections because they supported the laws.

There's never been a recall election for a Colorado state legislator.

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