How California got tough on guns

California has a reputation for being tough on guns. That reputation is well-earned.

Researchers at Boston University have counted 111 California laws that in some way restrict “the manner and space in which firearms can be used.” They include regulations on dealers and buyers, background check requirements, and possession bans directed at certain “high risk” individuals.

By their count, no other state out-regulates California when it comes to sheer quantity of rules. And we’ve held that top spot since at least 1991, the year the researchers started counting.

The Giffords Law Center To Prevent Gun Violence, a gun control advocacy group, ranked California No. 1 for strongest laws in its 2024 state gun law scorecard.

“There are not a lot of As out there,” said Ari Freilich, the organization’s California legislative affairs director. “California has driven the conversation nationally.”

In contrast, Guns and Ammo magazine has labeled California the fourth worst state for gun owners. (New York was the top jurisdiction, followed by New Jersey.)

The story of how California became, according to many, the state with the nation’s most restrictive gun laws has largely followed a familiar pattern:  alarm or tragedy, then a legislative response.

A history of gun control in California

• 1863 — Concealed carry ban: Includes daggers and “swords in canes”
• 1917 — Background checks and concealed carry permits: Dealers must share data with police
• 1923 — First major handgun law:
  • Felons, non-citizens banned
  • Dealer licenses
  • Serial numbers
  • One-day waiting period
• 1965 — Waiting period extended: 5 days for handguns
• 1967 — Loaded open carry ban: After armed Black Panthers visit capitol, Gov. Reagan signs ban for incorporated areas
• 1968 — U.S. Gun Control Act:
  • Nationwide rules
  • Vendor licensing
  • Minimum age requirements
• 1972 — Longer waiting period: 15 days for handguns
• 1982 — Prop. 15 fails: Measure to cap number of handguns
• 1989 — State assault weapon ban: Bans sale of 50+ models
  • Gunman kills 5 children in Stockton
• 1991 — Gun show loophole closed:
  • All sales through licensed dealers
  • Waiting periods for all firearms
  • 10 year ban for some gun offenses
• 1993 — Shooting in San Francisco: Man kills 9 at downtown law office
• 1994 — U.S. assault weapon ban: “Assault weapon” defined by gun features
  • In California, handgun buyers must pass written test, watch video or take course
• 1996 — Waiting period reduced: 10 days for handguns (current law)
• 2000 — Assault weapon ban boosted:
  • Defined by gun features
  • No new 10+ round magazines
  • 1 handgun per month
• 2002 — Handgun safety test: First-time buyers must pass exam given by local law enforcement
• 2004 — U.S. assault weapon ban expires: Sunsets after 10 years
• 2012 — Ban on unloaded handguns in public: State also starts collecting data on all sales
• 2013 — “Microstamping” rule for new semi-automatic pistols, ban on all unloaded guns in public
  • Gun rights sue
• 2014 — Tougher handgun safety test: Test for first-time buyers of any gun
• 2015 — San Bernardino mass shooting: 14 killed when couple go on rampage
• 2016 — Prop. 63 passes:
  • Ammo background checks
  • No mail orders
  • Bans all big magazines
• 2017 — Mag ban blocked and “ghost gun” shooting
  • Judge freezes ban
  • Shooter kills 5 in Tehama County using self-assembled guns
• 2018 — Another suit, another mass shooting
  • Gun groups sue over Prop. 63’s order-by-mail ban
  • CA Supreme Court upholds microstamping
  • Shooter kills 13 at Thousand Oaks bar
• 2019 — New governor, new rules
  • 21 year age limit
  • Lifetime ban for misdemeanor domestic violence
  • Mass shootings at the Gilroy Garlic Festival and Saugus High School
• 2020 — Legal limbo: Federal judge puts hold on ammunition background check requirement and large magazine ban. The 9th Circuit Court of Appeals restores the law and allows it to take effect.
• 2022 — Major Supreme Court case: The U.S. Supreme Court strikes down a New York City concealed carry law in a ruling that has major ramifications for state and local gun control policies.
• 2025 — About those background checks: The 9th Circuit Court of Appeals strikes down California’s ammunition background checks from Prop. 63, citing the new standard for gun control laws set by the U.S. Supreme Court in the New York concealed carry case. The 9th Circuit also overturned the California law that limited gun purchases to one per month.

Guns laws cover the who, what, where, when and how of buying, selling, lending, leasing, storing and firing guns. By national standards, California law is strict on just about all of these points.

Who can sell

• Licensed dealers only
• To qualify as a licensed dealer you must pass background check, earn a safety certificate and report all sales
• Gun show and other private sales must go through a licensed dealer

Who can buy

• Must pass an exam administered by the state Department of Justice
• Must wait 10 days between purchasing and receiving a gun
• Over age 21
• Must be a resident (handguns)

Who can’t own

• Lifetime ban for:
  • Many violent felonies and various domestic violence misdemeanors
  • Those involuntarily placed into mental health treatment twice in same year
• Ten year ban for certain misdemeanors
• Temporary ban for:
  • Those subject to restraining orders
  • A court can temporarily remove firearms from anyone charged with domestic violence

Ammo rules

• Anyone selling more than 500 rounds per month requires a license*
• Can only buy from licensed dealer*
• No online purchases for home delivery
• No magazines with 10+ rounds*
• Background check required*

*Currently held up in court

Where and how

• No carrying in open—loaded or not
• Concealed carry with permit only
• Concealed carry applicants must demonstrate “good moral character” and “good cause,” then pass a test
• No permit required for those who believe they are in “grave danger” from subject of a restraining order
• Otherwise, gun must be transported unloaded and in a locked container

What’s banned

• “Assault weapons,” which include all semi-automatic firearms without a fixed magazine and at least one suspect feature such as a protruding pistol grip
• Any “assault weapon” listed by state
• Post-1986 automatic weapons
• Handguns not listed on the state’s Roster of Handguns Certified for Sale
• Gun with no registered serial number
• Newly produced semi-automatic handguns without microstamping
• Sound suppressors and bump stocks

The United States is not an especially crime-ridden nation. Overall crime rates here are roughly on par with other high-income countries. Where the country stands out—way out—from its international peers is in gun violence.

The U.S. has a gun death rate (all causes of death, including suicide and accidental death) of roughly 14 per 100,000 people. According to research out of the University of Washington, that puts the U.S. in the company of Panama and the Dominican Republic.

Recently guns became the second leading cause of death of children and teens across the country.

At 8.2 gun deaths per 100,000, gun violence in California is much lower than the national average. But that isn’t particularly low by international standards. We have roughly the same gun fatality rate as South Africa. In 2023, 3,209 Californians were killed by guns, according to the CDC.

As in the rest of the country, gun violence in California is not equally distributed.

Firearm fatalities are a disproportionately male tragedy. According to research from UC Davis, men are more than seven times more likely to be killed by someone else with a gun than women. Men are also more than eight times more likely to take their own lives with a firearm.

While mass shootings seize public attention, they do not claim the most lives. Half of gun deaths in California are suicides — a disproportionate number of them among white men over the age of 50. Most gun homicides, meanwhile, are not high-profile acts of mass carnage, but random outbursts of violence that strike communities least likely to draw news crews.

Supporters of California’s rigorous gun controls have a pretty compelling argument on their side: California has tough gun laws and it has relatively low rates of gun violence. And that’s a relationship that generally holds true across all 50 states.

But as with any thorny sociological question—particularly one where lives, livelihoods, deeply held values and constitutional law all hang in the balance—it’s probably more complicated than that. 

Do tight gun laws lead to lower deaths? Or is it that states with less gun violence (due to different cultural attitudes about guns or varying economic and demographic patterns) are more likely to adopt tighter gun controls? 

There seems to be relatively strong evidence that denying firearms to at least certain “high-risk” individuals leads to lower levels of violence. Three separate studies found that in states that keep guns away from those under domestic violence restraining orders, gun homicide rates between partners are 9 to 25 percent lower. California has such a law on the books. A similar study found that denying guns to those with misdemeanor violent crime convictions reduced their chances of being rearrested for another violent crime by 30 percent. California has this type of gun ban in place too.

Do comprehensive background checks keep guns away from those who shouldn’t have them?

One study concluded California’s law had relatively little effect—suggesting vendors skirting the rules and lax enforcement could be why. But another study estimated that when states require gun vendors to get licensed, conduct background checks and are subject to inspection, gun homicides can be expected to fall by more than 50 percent. An overview of the research from the RAND Corporation found suggestive but “limited evidence that background checks reduce violent crime.”

And concealed carry laws?

A landmark economic study from the mid-1990s found evidence that making it easier for people to carry reduced crime, supporting the NRA’s “good guy with a gun” theory. But more recent research using the same statistical techniques but with a larger dataset claims to show the exact opposite.

“What probably has the greatest impact are a number of things acting together—just the pure volume of laws,” said Eric Fleegler, a pediatric emergency physician at Boston Children’s Hospital and professor at Harvard University. “We are studying legislation and not randomized control trials. But overall, when you look at systematic reviews of legislation on homicides and suicides, it is fairly clear that legislation designed to place reasonable restrictions on how firearms are sold or maintained or stored does lead to decreased fatality rates.”

California has long struggled to enforce some of the gun laws advocates hold up as models for the rest of the country. Case in point: the Armed and Prohibited Persons System.

Fifteen years ago, California became the first to launch a database to alert law enforcement when someone with a legally purchased firearm lost the right to have a gun. Today it’s still struggling to account for guns it believes are in the hands of people that society deems too dangerous to be armed.

And California officials don’t even know the size of the current backlog. The database is so clunky and outdated it’s unable to produce reports showing how many cases have been open more than six months.

“We’re no longer at the front of the pack here,” said Stephen Lindley, who spent more than 20 years in the state Justice Department’s Bureau of Firearms. “You can’t keep prohibiting people and not make sure they’re unable to get or maintain firearms.” 

Local law enforcement, frustrated by flaws in the data, have often ignored the system and left it up to a chronically understaffed unit of state agents. Many judges do little or nothing to ensure their relinquishment orders are followed.
California is also one of the only states with a formal process for removing guns from abusers who become the subject of a domestic violence restraining order in local family courts. But some judges fail to check Justice Department records to see if alleged abusers are armed. And even when judges are presented with evidence of a firearm, some rarely follow through to ensure the guns are surrendered.

―Robert Lewis

Gavin Newsom’s first press conference as governor-elect took place on the morning of November 8, 2018, just eleven hours after a gunman opened fire at the Borderline Bar and Grill in Thousand Oaks killing 13 people including himself. “The response is not just prayers,” Newsom said. “The response cannot just be more excuses. The response sure as hell cannot be more guns.”

A few days later he doubled down on Twitter, calling the National Rifle Association “a fraudulent organization” and “completely complicit” in the massacre.

No one familiar with Newsom’s career could have been surprised. He was the driving force behind Proposition 63, a 2016 ballot measure that put sweeping new restrictions on ammunition sales and banned high-capacity magazines (like the ones used in Thousand Oaks).

“We’re preparing for the worst,” said Chuck Michel, head of the California Rifle and Pistol Association.

Pro-gun arguments once resonated in California. In 1982, a proposition to cap the number of handguns^* in California lost by 63 percent of the vote—taking the gubernatorial campaign of Democrat Tom Bradley along with it. The reason, according to a Washington Post analysis from the time, was that “people who did not ordinarily bother with politics and politicians were coming out in droves to save their unrestricted right to bear arms.”

But that silent, well-armed majority failed to materialize in 2016 when Prop. 63 passed—also with 63 percent of the vote.

Nearly two-thirds of respondents in a recent survey from the Public Policy Institute of California said that gun laws should be “more strict” than they are now. Included in that group were 49 percent of the conservatives surveyed.

According to Craig DeLuz, the California director of legislative affairs for the Firearms Policy Coalition, those numbers reflect a misconception of what’s already on the books.

“If there are reasonable firearms regulation out there, we’ve already passed that point,” he said. “A lot of people are completely unaware that most of the things that the average voter believes to be ‘reasonable’ are already in place in California.”

California is often considered the innovation hub of the United States. Why should it be any different for guns?

The state’s tough firearm laws have led “many entrepreneurs to ‘innovate’ ways around the law,” said Ari Freilich of the Giffords Law Center To Prevent Gun Violence.

Consider the case of the bullet button.^* In 2001, California expanded its ban on new “assault weapons”^* to include any modern semi-automatic rifle^* with a detachable magazine^* and at least one of a handful of other features, including a protruding pistol grip^* or an adjustable stock^*. To get around the ban, many gun owners came up with a solution: install a small lock on the magazine that can be easily opened with a small tool (or the tip of a bullet). Legally speaking, that tiny bit of hardware would transform a contraband assault weapon with a detachable magazine into a perfectly legal rifle with an ever-so-slightly-less detachable magazine.

In 2017, California lawmakers caught on and amended the law. That prompted the development of yet another workaround device: the Patriot Pin. And so the arms race over arms design continues in California.

With so many regulations now in place on newly manufactured firearms, many gun enthusiasts are simply building their own guns—or at least, they’re putting together the final pieces.

One of the most popular firearm products in California are “80 percent” or “unfinished” receivers.^* Receivers are the central frame of a firearm onto which all the other components are connected. “Unfinished” simply means it lacks a few cavities and holes. But legally, that makes all the difference. Under both federal and California law, an unfinished receiver is just an elaborately shaped piece of metal. Under a law passed in 2016, Californians with home-finished receivers were given until January 1st of 2019 to register their gun with the state. It’s not clear how widespread compliance has been.

Still, plenty of lawmakers are worried about the spread of unidentifiable “ghost guns.” In 2017, a man with two home-built semi-automatic rifles killed five people and shot up an Elementary School in Tehama County. In 2019, a man killed a highway patrol officer in Riverside County with a home-assembled AR-15-style rifle. A student at Saugus High School in Santa Clarita also used a kit-assembled weapon to murder two fellow schoolmates before killing himself. In 2016, a proposal to designate unfinished receivers as legal “firearms” passed both the Assembly and Senate, but was vetoed by Gov. Jerry Brown.

“By defining certain metal components as a firearm because they could ultimately be made into a homemade weapon, this bill could trigger potential application of myriad and serious criminal penalties,” Brown wrote in his veto message.

But with a new governor came a new approach. In 2019, Gov. Newsom signed a law requiring anyone hoping to purchase an unfinished receiver to undergo a background check. The law didn’t go into effect until 2024.

And in 2021, newly-elected president Joe Biden followed suit. In early April, Biden announced three new executive orders aimed at curbing gun violence. One would require unfinished receivers to be etched with a serial number and subject ghost gun purchasers to a background check.

California’s Department of Justice is holding the line as gun rights advocates push back in ways that could have dramatic consequences for state law.

Duncan v. Bonta

In 2016, state voters passed Proposition 63, which banned magazines with a capacity to hold 10 rounds or more. Though a 2000 law restricted the sale and manufacture of new high-capacity magazines, existing owners had been grandfathered in. Prop. 63 effectively un–grandfathered them. Five gun owners and the California Rifle & Pistol Association (the state branch of the National Rifle Association) sued. In 2019, U.S. District Judge Roger Benitez issued a searing opinion, holding that the Second Amendment also applies to commonly-owned high-capacity magazines. “Without a right to keep and bear…the magazines that hold ammunition, the Second Amendment right would be meaningless,” he wrote. On Nov. 30, 2021, the full 9th Circuit eventually overruled Benitez and upheld the ban, ruling that limiting the size of magazines does not significantly interfere with the right to self defense. But on June 30, 2022, the U.S. Supreme Court tossed out that 9th Circuit decision, ordering the appellate judges to reconsider the case in light of the highest court’s concealed carry decision (see below), which sets a new, stricter standard to legally justify firearm restrictions.

Rhode v. Becerra

Prop. 63 also requires Californians to get their ammo only from state-licensed vendors in face-to-face transactions. Out-of-state vendors hoping to get into the California cartridge* market are therefore required to go through a certified California vendor to broker the transaction. A lawsuit filed by the California Rifle & Pistol Association (NRA) and California-born Olympic skeet shooter Kim Rhode contends the new law puts an excessive burden on “interstate commerce” and that it violates the Second Amendment. In April 2020, the same federal district judge who slapped the state down in the Duncan case put a hold on the background check law writing that such checks “do not work,” that “every law-abiding responsible individual citizen has a constitutionally-protected right to keep and bear firearms and ammunition” and that Prop. 63 is “precisely what the Bill of Rights was intended to protect us from – a majority trampling upon important individual rights.” The state appealed the ruling to the 9th Circuit U.S. Court of Appeals. In March 2021, three judges from the court put the proceedings on hold to wait for a ruling in the Duncan case. A 2022 U.S. Supreme Court ruling against a New York City concealed carry law led the 9th Circuit to reconsider the case several years later. In 2025, a three-judge panel on the appeals court struck down the background checks.

Pena v. Horan

Since 2001, California has only allowed handguns to be sold, imported, or manufactured in California if they are considered “not unsafe” by the state. The Department of Justice maintains a list of these approved firearms, known as the “roster.”^* In 2009, gun rights activists sued, arguing that the roster impinges on gun owners’ Second Amendment rights and that the rationale the state uses to keep certain guns off the list is “arbitrary and capricious.” In recent years, as the state has placed more restrictions on new firearms, opponents of the roster have said it amounts to a “slow-motion handgun ban.” On June 15, 2020, the U.S. Supreme Court declined to take up the case.

State of Washington v. United States Department of State

In 2015, the U.S. State Department settled a case with the Texas nonprofit Defense Distributed, allowing it to publish its 3D-printable gun designs online. California joined a multi-state lawsuit filed by the State of Washington against the federal government. The states argue that allowing the release of those codes violated their right to regulate firearms within their own borders. In November 2019, a federal judge sided with the states. But this being the Internet, the files are out there.

New York State Rifle & Pistol Association v. New York

The U.S. Supreme Court in early 2019 agreed to hear a constitutional challenge to a New York City law that did not allow most handgun^* owners to take their firearm outside their homes unless they’re going to an authorized shooting range and barred them from taking their guns outside the city entirely. California had a lot at stake in the outcome. In 2010 the Supreme Court affirmed every American’s individual right to bear arms “in the home for the purpose of self-defense.” An expansive ruling on the case from New York, as some court watchers initially predicted, could find that the right to bear arms exists outside the home as well, potentially sweeping away California’s restrictions on both open and concealed carry in a single decision. “Winter may very well be coming for gun laws in California,” the head of the California Rifle and Pistol Association, Chuck Michel, told NRATV. “We may be able to knock more than a few of those out.” The U.S. Supreme Court in 2022 ruled against New York City, striking down its concealed carry law.

Jones v Becerra

Pro-gun rights advocates, two 20-year-old gun enthusiasts and a handful of gun shops sued the State of California in July 2019, arguing that a new state law setting the legal gun-purchasing age at 21 unjustifiably “prohibits an entire class of adults from exercising their Second Amendment right to keep and bear arms.” The law in question was authored by Sen. Anthony Portantino, a Democrat from La Cañada Flintridge, and signed by Gov. Jerry Brown in late 2018. It extended the age limit from handguns to all firearms, but some exceptions remain for young police officers, members of the military and anyone with a valid hunting license. 

Miller v Becerra

Building off an early victory in Duncan v Becerra, when a district court judge held that the state’s ban on large capacity magazines violates that Second Amendment, gun rights groups from San Diego doubled down, challenging California’s entire “assault weapon” ban on the same grounds. The 19-year-old ban defines an assault weapon as any semiautomatic rifle with some combination of suspect features, including a detachable magazine. Because the court already froze the state’s large magazine ban, the San Diego County Gun Owners Political Action Committee argues, any law that forbids the purchase of a weapon based on its use of such a magazine must also be unconstitutional. 

On June 4, 2021, Roger Benitez, the same federal district judge who struck down the state’s ban on large magazines, sided with the San Diego gun owners. In a lengthy and scalding opinion, he called California’s assault weapons ban a “30-year-old failed experiment” and ruled that the Second Amendment only allows firearms to be banned outright in “extreme cases,” such as “bazookas, howitzers, or machineguns.”

Attorney General Rob Bonta appealed, and on June 21, 2021, a federal appeals court blocked Benitez’s ruling.

New York State Rifle & Pistol Association v. Bruen

New York, like California, is one of just a handful of states where applicants for a license to carry a concealed handgun must not only meet statutory requirements, but prove that they have a special need. In June 2022, the U.S. Supreme Court struck down that regulatory approach as unconstitutional and held that the right to “keep and bear arms” includes the right to bear a firearm outside in public. The opinion also makes it more difficult for governments to justify gun restrictions of any kind, by requiring them to “demonstrate that the regulation is consistent with this Nation’s historical tradition.” Legal experts consider it one of the most sweeping gun rights rulings in more than a decade.   

Guns are complicated. So is gun policy. Here are some terms and phrases to help you make sense of it all.

AR-15-style rifle: A particularly popular style of semi-automatic rifle, this one is based on the original ArmaLite AR-15, built for U.S. military in the late 1950s which relabeled it the M-16. Since the expiration of the AR-15 patent, many manufacturers have produced a wide array of similarly designed, modular semi-automatic rifles. The AR-15 style is among the most popular in the United States. People who aren’t gun enthusiasts will likely recognize it as the weapon of choice for mass shooters at San Bernardino, California; Sandy Hook, Connecticut; Parkland, Florida; and Las Vegas, Nevada.

Assault rifle: A rifle capable of fully automatic and semi-automatic modes of fire. Based on this definition, federal law prohibits civilians from owning assault rifles manufactured after 1986. However, other definitions are occasionally used. Adding to the confusion, an “assault rifle” is not the same thing as an “assault weapon” (see below).

Assault weapon: A nebulous, politically-charged term that dates back to at least 1980. California law offers a wide-ranging definition that encompasses any “semi-automatic, centerfire rifle” with a detachable magazine and at least one of a handful of other features, including a protruding pistol grip or an adjustable stock. This mix and match approach to defining a banned weapon has led to some creative workarounds from gun enthusiasts. But California also explicitly includes a number of makes and models in its ban, including the original AR-15 and other high-powered rifles. Gun control activists argue that the term “assault weapon” is a useful term to describe a weapon with enhanced killing power, while gun rights advocates dismiss it an imprecise catch-all designed to turn the public against any firearm that happens to looks like an assault rifle, regardless of its actual lethality.

Automatic: A firearm or firearm setting that will allow the gun to be fired continuously until the trigger is released or the gun runs out of ammunition.

Bullet: A projectile shot from a firearm. A bullet is one component of a complete round or cartridge. To reiterate: a bullet is not a cartridge.

Bullet button: A magazine release that can only be activated with a pointed tool or the tip of a bullet (hence the name). These devices were invented to convert a firearm with a detachable magazine into a firearm with slightly-less detachable magazines so as to comply with California’s assault weapon ban. California includes a detachable magazine as one of the components in its definition of restricted weapons. A 2017 state law effectively closed the “bullet button loophole,” meaning that any firearm with the device is still legally considered to have a detachable magazine and therefore, possibly, an assault weapon.

Bump Stock: An adjustable rifle stock that uses the force of the firearm’s recoil to allow the trigger to be repeatedly pulled. A kind of multiburst trigger activator, this effectively allows a semiautomatic weapon to simulate automatic fire. Bump stocks gained national attention after a shooter used one to kill nearly 60 people and wound hundreds more in Las Vegas in 2017. They are banned by both federal and state law.

Caliber: The diameter of a cartridge (or sometimes the bore of a firearm itself). Typically measured as fractions of an inch (for example, .22) or millimeters (for example, 9 mm).

Cartridge: A unit of ammunition for a firearm that often includes a bullet, primer and propellent (i.e. gunpowder) within a casing. Also called a “round.” To reiterate: a cartridge is not a bullet.

Casing: The metal container for a unit of ammunition. Sometimes called a “shell.”

Clip: A device used to hold multiple rounds together, which allows multiple rounds to be loaded into a firearm with an internal magazine at once. Clips are rarely used today except with older long guns.

Centerfire: A round-type that, when fired, is struck by the firing pin in the center of the back—used in most modern firearms as the rounds can accept higher power (as opposed to rimfire).

Concealed carry license: California is one of eight states that allow civilians to carry a concealed weapon only if local law enforcement agencies decide to give them a permit. This distinguishes California from “shall issue” states, in which concealed carry permits must be issued as long as an applicant meets the legally specified requirements, and “permitless” or “right to carry” states where no permit is required.

Gauge: A unit of measure for the diameter of a firearm barrel, typically used for shotguns. The origin is slight anachronistic: a gauge refers to the number of lead balls that one could snuggly fit inside the barrel of the gun if only drawing from one pound of lead. In other words, the smaller the gauge, the bigger the gun.

Gun Show Loophole: Under federal law, individuals can sell firearms without a license as long as they don’t make a living off the trade. These amateur sellers are not subject to federal requirements—namely, that they must conduct background checks on their purchasers. In California, all sales must be conducted through a licensed vendor, closing the “loophole.”

Handgun: California defines a handgun as “any pistol, revolver, or firearm capable of being concealed upon the person.” Also sometimes a “short-barreled rifle or a short-barreled shotgun.”

Handgun Roster: California law bans the sale or manufacture of any handgun that doesn’t meet state safety standards. According to data compiled by the CalGuns Foundation, a gun rights organization, the number of firearms on the list has declined each year since 2013. As of the end of January 2019, there were over 700 models on the list.

Magazine: A spring-loaded device used to hold multiple rounds designed to load each round into the firearm’s firing chamber with a spring. Some firearms have internal magazines into which ammunition must be manually loaded, while others have detachable magazines which allow for quicker unloading and reloading.

Microstamp: Any technology that stamps a unique identifying mark on the round casing when the gun is fired. In theory, this acts like a fingerprint, allowing law enforcement to track an empty shell at a crime scene to a particular gun. California law requires all new semi-automatic pistols sold in the state to include microstamping technology. Gun advocates argue that the technology is untested and prohibitively expensive for manufacturers to implement and that the law is effectively a “backdoor ban” on an entire class of newly manufactured firearms.

Multiburst trigger activator: Any enhancement that allows a semi-automatic weapon to fire multiple rounds with each pull of the trigger simulating automatic fire. A bump-stock is a notable example. Other devices use recoil, a crank, or internal mechanisms to the same effect.

Pistol: A handgun in which the chamber that holds that ammunition is part of the barrel. This is opposed to a revolver.

Pistol Grip: A grip that extends beneath the receiver allowing the shooter to hold and fire the weapon like a pistol (with a straight wrist). Under California law, a “pistol grip that protrudes conspicuously beneath” the weapon can be one of the defining features of an “assault weapon.”

Revolver: A handgun in which the chambers holding ammunition revolve around a cylinder.

Rimfire: A round that can be fired by striking anywhere on the back of the round—rarely used today except for low powered firearms. As opposed to centerfire.

Receiver: The frame of the gun that houses the firing mechanisms. Under U.S. federal law, this is considered the firearm and regulated as such.

Semi-automatic: A firearm that will fire a single shot and then automatically load a new round into the chamber each time the trigger is pulled.

Stock: The rear portion of a rifle or shotgun that is often held to shoulder for support.

Unfinished Receiver: The frame of the gun that houses the firing mechanisms, but which lacks a channel or pocket for the gun’s firing mechanism. Once those modifications have been made with a drill press or another tool, the receiver is legally considered a firearm (though only legally; additional components are required before it can shoot). Also called “80 percent lower receivers.”