(WASHINGTON) — For nearly 11 months, firearm manufacturers and gun control advocates have waited as a major “ghost gun” regulation has snaked its way through federal regulation processes, inching closer toward implementation.

Meanwhile, each year since 2016 has seen growing numbers in untraceable firearms to date, according to Bureau of Alcohol, Tobacco, Firearms and Explosives statistics— in schools, makeshift factories and rising crime scenes as some state legislatures have scrambled to act, in what Everytown for Gun Safety’s president called “the most unregulated corner of the firearms industry.”

In the coming months, a measure that will modify the federal definition of “firearm” to include unfinished gun parts like frames and receivers is expected to receive approval. The Justice Department introduced the proposal last May in an effort to curb the rise of so-called ghost guns — unregulated, easy-to-make firearms that can be ordered online. Ghost guns often come in kits and many can be assembled within an hour.

The modified definition is meant to disrupt a supply chain that has strengthened over the past five years, gun control experts said. The number of unserialized (and thus unregulated) firearms seized by major metro police departments has grown exponentially. In Philadelphia, local police seized 571 ghost guns in 2021 compared to 13 in 2018. In New York City, police seized 375 ghost guns in 2021 compared to 48 in 2019, according to city data.

“I could spend hours telling these stories about how these ghost guns have hurt our community and made our streets unsafe,” Baltimore Police Chief Michael Harrison, whose department seized nine ghost guns in 2018 compared to 352 in 2021, said at a January press conference.

From 2016 through 2020, there were approximately 23,906 suspected ghost guns recovered by law enforcement from potential crime scenes, according to the DOJ. Without a serial number, it is often impossible for law enforcement to track where individual guns came from.

“There’s no question about it, that the regulation will shut down the marketplace going forward,” John Feinblatt, president of Everytown for Gun Safety, told ABC News.

National Shooting Sports Foundation general counsel Lawrence Keane said in an interview that the regulation is “the single most significant change for manufacturers under the law, since the Gun Control Act was enacted in 1968.”

So far, 10 states and Washington, D.C., have enacted laws to disrupt the supply chain of ghost guns. Last year’s DOJ proposal came after several lawsuits from gun control advocates and a letter from 18 state attorneys general urged U.S. Attorney General Merrick Garland to propose such a change.

“While states can close this loophole within our own borders, we need federal action to institute a nationwide solution; even when states try to close this loophole, 80% receivers can still be readily purchased online, or trafficked into our states from other jurisdictions,” the AG’s said in the letter.

This is in reference to the “80% rule” — namely, that frames and receivers that are 80% completed are not technically considered firearms under current rule and are not regulated by the Gun Control Act of 1968. They’re unserialized, untraced and can be ordered online by those barred from buying a traditional firearm. “80% receivers” often come in kits with the other parts necessary to build a ghost gun. 3D printers can also produce ghost gun parts.

Lobbyists on behalf of the firearm industry and gun control measures expect the new regulations to come into place with possible revisions based on the nearly 300,000 public comments received.

When exactly that will come, however, is up in the air.

In a statement to ABC News, the DOJ said the original agenda lists June 2022, but “we are working to finalize it as soon as feasible.” Acting ATF director Marvin Richardson also said at an NSSF gathering that the expected date is June.

But Feinblatt, the Everytown president, told ABC News the White House said the regulations will come in April.

Once finalized, it will be the first time the definition of “firearm” will be changed since the Gun Control Act of 1968.

“I’ll say it’s the single most important thing that can be done on the ghost gun issue,” David Pucino, deputy chief counsel of Giffords, an organization that monitors and advances gun control legislation and founded by former Rep. Gabrielle Giffords, told ABC News.

Pucino said his office has monitored ghost guns since 2017 in California, which is where ghost guns first sprouted. Due to California’s strict gun control laws, he said unserialized firearms became increasingly popular.

“Somewhat perversely, the states that have the strongest gun laws are the ones that are most susceptible to ghost guns,” Pucino said. “Because it’s the easiest route to get around all those regulations in place.”

Already, the proposed changes have been met with pushback from the firearms trade industry. Keane, from the NSSF, said in an interview with ABC News that the proposed definition overreaches ATF’s statutory authority. Many of the new implementations, such as multiple or reprinted serial numbers on guns, a manufacturing overhaul and unclear implementation details, overstep the ATF’s authority, he said.

Keane also said the 90-day period from when the rule is implemented to when firearm manufacturers have to comply is too short for major changes to the law.

“So (the ATF) indicated that the comments from (the firearm) industry were helpful, and made them think about things they hadn’t considered or thought about,” he said.

He expects to see modifications from last year’s proposed changes. “We’ll see what the final rule says,” Keane added.

Cracking down on ghost guns is a key part of President Joe Biden’s agenda in curbing gun violence.

During a trip to New York City following the deaths of two NYPD officers, he announced the creation of a National Ghost Gun Enforcement Initiative, including a strike force to crack down on illegal gun trafficking across state lines.

At the State of the Union, Biden brought up the issue again.

“… we’ll do everything in my power to crack down on gun trafficking, on ‘ghost guns’ that you can buy online, assemble at home, no serial numbers, can’t be traced,” he said.

Once the regulation is implemented, “that will cut off ghost guns at the source,” Pucino said.

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