Police
said more than 100 rounds were fired by multiple people during the Sacramento shooting. One of the weapons, they said, was a handgun that had been illegally modified so that it qualifies as a "machine gun" under California law,
meaning a weapon that "shoots, is designed to shoot, or can readily be restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger." California
prohibits possession of such firearms without a special, rarely issued permit, and they are
strictly regulated under federal law, which has banned sales of newly produced machine guns to civilians since 1986.
What about requiring "background checks on all gun sales"? California has required "universal background checks," covering private transfers as well as sales by federally licensed dealers, since 1991. A
2019 study found that requirement "was not associated with a net change in the firearm homicide rate over the ensuing 10 years in California."
Another study suggested that such requirements are widely disregarded, finding that background checks increased when Delaware enacted a law like California's but not when Colorado and Washington did.
The problem, according to Everytown for Gun Safety, is that many states do not mandate universal background checks, which is why we need a
federal law imposing that requirement on the entire country. But there is little reason to think that people will be more inclined to follow this requirement, which in practice means that all gun transfers have to be mediated by a federally licensed dealer, simply because Congress joins California et al. in saying they should. More to the point, it is hard to see how such a requirement is relevant to what happened in Sacramento.
The converted handgun that police recovered after the shooting was
stolen, which is not the sort of transfer that would be affected even by perfect compliance with a law requiring "background checks on all gun sales." According to a
2019 study by the Bureau of Justice Statistics, just 10 percent of guns used in crimes were obtained from a "retail source" such as a gun store, a pawn shop, a flea market, or a gun show. Nine out of 10 were obtained from informal sources, including friends or relatives, the "underground market," and theft.
It makes sense that criminals would prefer such sources, especially if they have felony records that disqualify them from legally possessing firearms. But given these longstanding workarounds, expanding background-check requirements so that they notionally cover all transfers cannot reasonably be expected to have a significant impact on criminals' access to guns.