Aside from the obvious "black market" and gun show loopholes (which I doubt gang members or drug dealers utilize directly although those who might sell to them probably do), you basically have a whole issue of "ghost guns" that are assembled from parts, most of which do not need to be registered.
The Daily 202: Police officers keep getting shot by people with criminal records who are not allowed to own guns
By James Hohmann
August 15 at 11:23 AM
THE BIG IDEA: The man who allegedly shot six police officers in Philadelphia before surrendering just after midnight, following a 7½-hour standoff that ended when tear gas was fired into his home, has a very long rap sheet that makes it a felony for him to possess a firearm. That clearly didn’t stop him. It is part of a pattern that underscores how difficult it is to curb the epidemic of gun violence, even when there is political will. Despite the laws that are already on the books, criminals find ways to acquire weapons without background checks — whether at lax stores, through the gun show loophole, via the Internet or on the black market. This is possible, in part, because it’s breathtakingly easy for most Americans to legally acquire guns. Nevertheless, it’s a challenge that policymakers must grapple with as they debate new forms of gun control.
A California highway patrolman was killed by a felon on Monday night, and two of his colleagues were badly wounded, during a gun battle after a traffic stop on the freeway in Riverside. The shooter used an AR-15 assault-style rifle without a serial number, which makes it untraceable, according to the Los Angeles Times. These “ghost guns” are assembled from parts that can be ordered by mail or obtained underground, and ATF reports that about a third of all firearms seized in California now are un-serialized. Agents expect this number to grow.
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-- The Riverside cop killer, Aaron Luther, previously pleaded guilty to attempted murder and two counts of burglary. He had also been convicted of unlawful possession of a firearm, as well as assault with a deadly weapon, spousal abuse, disturbing the peace, vandalism, battery and stalking. Luther was killed by police during an extended firefight on the 215 Freeway. Before he died, CHP Officer Andre Moye was able to return fire and radio for help. Luther’s father told KTLA that his son was a “desperate man.” His wife told the Riverside Press-Enterprise that he called her after he was pulled over and sounded panicked about going back to prison. Other family members said he had been battling depression.
-- Ghost guns like the one that Luther used can be legal for those who are allowed to own firearms, but Luther’s prior convictions barred him from owning weapons. “But California requires that anyone building a weapon apply for a unique serial number with the state’s Department of Justice and that number be put on the firearm,” today’s L.A. Times notes: “The weapon must comply with California’s laws governing firearms. Police gun experts say that those forbidden from purchasing a gun can still buy the partial lower receiver, known as an ‘80% lower,’ and then buy the other parts of the weapons. In 2013, John Zawahri killed five people in the Santa Monica area using an AR-15-style rifle, which he built from a partially manufactured lower receiver that did not have a serial number and therefore did not have to be registered. … A serial number is issued only to the lower receiver of a weapon. Some lawmakers in California are seeking to require a background check for all gun parts to stifle the trade-in ghost guns.”
https://www.washingtonpost.com/news/powerpost/paloma/daily-202/2019/08/15/daily-202-police-officers-keep-getting-shot-by-people-with-criminal-records-who-are-not-allowed-to-own-guns/5d54d17b88e0fa79e5482001/?wpisrc=nl_daily202&wpmm=1
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