From the article: "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.”
https://apnews.com/396bbedbf4963a28bda99e7793ee6366
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.”
https://apnews.com/396bbedbf4963a28bda99e7793ee6366