Design of AR-15 could derail charges tied to popular rifle

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This photo provided by the U.S. Department of Justice shows AR-15 lower receivers, which federal agents have seized, including these unfinished ones taken in 2014 in California, for firearms investigations nationwide. For decades, the federal government has treated the mechanism called the lower receiver as the essential piece of the semiautomatic rifle, which has been used in some of the nation's deadliest mass shootings. But some defense attorneys have recently argued that the part alone does not meet the definition in the law. (U.S. Department of Justice via AP)

DALLAS, TX – A subtle design feature of the AR-15 rifle has raised a technical legal question that is derailing cases against people who are charged with illegally buying and selling the gun's parts or building the weapon.

At issue is whether a key piece of one of America's most popular firearms meets the definition of a gun that prosecutors have long relied on.

For decades, the federal government has treated a mechanism called the lower receiver as the essential piece of the semiautomatic rifle, which has been used in some of the nation's deadliest mass shootings. Prosecutors regularly bring charges based on that specific part.

But some defense attorneys have recently argued that the part alone does not meet the definition in the law. Federal law enforcement officials, who have long been concerned about the discrepancy, are increasingly worried that it could hinder some criminal prosecutions and undermine firearms regulations nationwide.

"Now the cat is out of the bag, so I think you’ll see more of this going on,” said Stephen Halbrook, an attorney who has written books on gun law and history. “Basically, the government has gotten away with this for a long time.”

Cases involving lower receivers represent a small fraction of the thousands of federal gun charges filed each year. But the loophole has allowed some people accused of illegally selling or possessing the parts, including convicted felons, to escape prosecution. The issue also complicates efforts to address so-called ghost guns, which are largely untraceable because they are assembled from parts.

Since 2016, at least five defendants have challenged the government and succeeded in getting some charges dropped, avoiding prison or seeing their cases dismissed entirely. Three judges have rejected the government's interpretation of the law, despite dire warnings from prosecutors.

Federal regulations define a firearm's “frame" or "receiver” as the piece considered to be the gun itself. But in an AR-15, the receiver is split into upper and lower parts — and some of the components listed in the definition are contained in the upper half. That has led judges to rule that a lower receiver alone cannot be considered a gun.