Owning a .300 Blackout in California is legal, but the rules apply to the firearm’s configuration, not the cartridge. California does not ban any caliber. What the state regulates is how a rifle or pistol chambered in .300 Blackout is built, how its magazine is fed, how long its barrel is, whether it wears a suppressor, and how you buy the ammunition that feeds it. Get the configuration right and you can shoot .300 Blackout here without issue. Get one part wrong and you can be holding a felony.
Rifle Configuration: Featureless or Fixed Magazine
Under Penal Code 30515, a semi-automatic centerfire rifle with a detachable magazine becomes an assault weapon if it also carries any one of the following: a pistol grip that protrudes below the action, a thumbhole stock, a folding or telescoping stock, a flash suppressor, a forward pistol grip, or a grenade or flare launcher.1California Legislative Information. California Code PEN 30515 – Assault Weapons and .50 BMG Rifles A centerfire rifle with a fixed magazine holding more than 10 rounds also qualifies, as does any semi-automatic centerfire rifle under 30 inches overall.
Most California owners pick one of two builds to stay outside that definition.
Featureless Build
Strip every listed feature. Replace the standard pistol grip with a fin grip or similar compliant grip, install a fixed stock instead of a collapsible one, and swap any flash suppressor for a muzzle brake or compensator. With none of those features present, the rifle can run a standard detachable magazine.
Fixed Magazine Build
Keep the pistol grip, adjustable stock, and other ergonomics you want, but lock the magazine in place. Penal Code 30515 defines a fixed magazine as one “contained in, or permanently attached to, a firearm in such a manner that the device cannot be removed without disassembly of the firearm action.”1California Legislative Information. California Code PEN 30515 – Assault Weapons and .50 BMG Rifles Many owners install a device that requires the upper receiver to pivot open before the magazine release engages. Reloads are slower; you keep the features.
Be precise with either path. Swapping a muzzle brake for a flash hider on a rifle with a detachable magazine is enough to trigger a violation. Most people who run into trouble do so by not realizing that a single part swap has just reclassified their rifle.
AR Pistols Chambered in .300 Blackout
AR-platform pistols in .300 Blackout carry an additional layer of restriction. California maintains a roster of handguns certified for sale under Penal Code 32000.2California Legislative Information. California Code PEN 32000 – Rules Governing Unsafe Handguns Nearly all AR-style pistols are absent from that roster, so a dealer cannot sell you one new. Some owners acquire them through private party or intrafamilial transfers, each with its own procedural requirements.
Buyers once used a single-shot exemption, purchasing a pistol configured to fire one round at a time and then converting it. The California Department of Justice now warns that converting a single-shot pistol to semi-automatic operation may constitute manufacturing an unsafe handgun under Penal Code 32000, or manufacturing an assault weapon, depending on the resulting configuration.3State of California – Department of Justice. Handguns Certified for Sale That route is no longer the safe workaround it once appeared to be.
If you do legally possess an AR-platform pistol in .300 Blackout, assault weapon rules still apply. Because the AR pistol’s magazine well sits outside the pistol grip, a semi-automatic version with a detachable magazine is automatically an assault weapon under Penal Code 30515.1California Legislative Information. California Code PEN 30515 – Assault Weapons and .50 BMG Rifles There is no featureless workaround for this design. The magazine must be fixed, requiring disassembly of the action to remove it.
Short Barrels and Suppressors Are Off the Table
.300 Blackout was designed to shine in short barrels and with a suppressor. Both configurations are prohibited in California.
Short-Barreled Rifles
A short-barreled rifle in California is any rifle with a barrel under 16 inches or an overall length under 26 inches.4California Legislative Information. California Code PEN 17170 – Short-Barreled Rifle Possession is punishable by up to one year in county jail or a state prison term of 16 months, two years, or three years.5California Legislative Information. California Code Penal Code 33215 – Restrictions Relating to Short-Barreled Rifle or Short-Barreled Shotgun California does not honor federal NFA tax stamps for short-barreled rifles. ATF approval and a $200 stamp change nothing here.
Suppressors
California bans all silencers under Penal Code 33410. Possession is a straight felony carrying 16 months, two years, or three years in state prison, a fine up to $10,000, or both.6California Legislative Information. California Code PEN 33410 – Possession of Silencer Federal NFA registration does not override the state ban. California is one of only eight states that prohibit civilian suppressor ownership entirely. If you move here from a state where you legally owned one, you cannot bring it.
Magazine Capacity: 10 Rounds, Period
California prohibits manufacturing, importing, selling, or possessing any magazine that holds more than 10 rounds. Penal Code 32310 makes receiving or buying a large-capacity magazine punishable by up to one year in county jail or a state prison sentence.7California Legislative Information. California Code PEN 32310 – Large-Capacity Magazine Simply possessing one, even if bought legally elsewhere, is at minimum an infraction with a $100-per-magazine fine, and can be charged as a misdemeanor with jail time.
The 10-round ceiling applies to rifles and pistols alike. A .300 Blackout rifle on a fixed-magazine build still cannot carry more than 10 rounds in that fixed magazine, because a fixed magazine over 10 rounds creates a separate assault weapon classification under Penal Code 30515.1California Legislative Information. California Code PEN 30515 – Assault Weapons and .50 BMG Rifles The ban has been challenged in court, most recently in Duncan v. Bonta, but until the Supreme Court issues a decision the limit is fully enforceable. Betting on a future ruling is not a legal defense.
Buying .300 Blackout Ammunition
You can buy .300 Blackout ammunition in California, but every purchase runs through a licensed vendor with a Department of Justice eligibility check. Penal Code 30370 sets this up.8California Legislative Information. California Code Penal Code PEN 30370 – Ammunition Purchase Authorization
The check works two ways. If you already have a firearm registered in the state’s Automated Firearms System, the vendor runs a standard eligibility check, currently $1, with a DOJ proposal to increase the fee to $5.9State of California – Department of Justice – Office of the Attorney General. Regulations – Ammunition Purchase Fee If you don’t appear in the system, you’ll need a basic eligibility check, which costs more and takes longer because the DOJ has to verify your identity and eligibility from scratch.
Ammunition cannot be shipped to your home. All purchases, including online orders, must be routed to a licensed ammunition vendor for a face-to-face transaction.10California Legislative Information. California Code PEN 30312 – Ammunition Sales and Transfers Most California shooters buy in bulk to keep trips and per-transaction fees down.
Hunting with .300 Blackout
.300 Blackout is a capable hunting round for medium game at moderate range, and California hunters can use it. Since July 1, 2019, however, California has required non-lead ammunition for all hunting statewide, covering game mammals, game birds, and nongame species. A first violation is an infraction with a $500 fine; second and subsequent offenses carry fines between $1,000 and $5,000.11California Legislative Information. AB 711 Assembly Bill – Enrolled
Standard lead-core range ammunition cannot be used in the field. You’ll need copper or another certified non-lead load for hunting. Non-lead .300 Blackout options exist from several manufacturers, but they cost more and are not stocked at every retailer, so factor availability into your planning.
Building Your Own .300 Blackout
Home builds are a common route into .300 Blackout, especially for pistols that aren’t on the handgun roster. Federal law lets individuals manufacture firearms for personal use without a federal firearms license, and the ATF does not require individuals to serialize privately made firearms.12Bureau of Alcohol, Tobacco, Firearms and Explosives. Privately Made Firearms
California is stricter. Under Penal Code 29180 and related sections, anyone who manufactures or assembles a firearm in the state must first apply to the DOJ for a unique serial number, engrave that number on the firearm, and notify the DOJ within specified timeframes. Possessing an unserialized firearm is a misdemeanor. These rules apply to rifles and pistols regardless of caliber, and the finished firearm still has to meet every other configuration rule. Building your own is not an exemption from the assault weapon laws, the fixed magazine rule, or anything else on this page.
Buying from a Dealer: Waiting Period and Fees
When you buy any firearm in California, including a .300 Blackout rifle, the dealer submits a Dealer Record of Sale to the DOJ. The state collects a total fee of $37.19, covering the background check, transfer registry, and associated safety fees.13State of California – Department of Justice – Office of the Attorney General. Frequently Asked Questions A 10-day waiting period runs between purchase and possession. There is no exception for existing firearm owners or concealed carry permit holders on standard purchases. Private party transfers go through a licensed dealer and are subject to the same waiting period and fees.
Between DROS fees on the firearm, ammunition background checks on every purchase, premium pricing on compliant parts like fin grips and fixed-magazine devices, and the higher cost of non-lead hunting rounds, running a .300 Blackout in California costs meaningfully more than in most other states. None of it is optional if you want to stay legal.
Penalties for Getting It Wrong
Consequences escalate quickly with the violation.
- Possessing an assault weapon under Penal Code 30605: a first offense involving no more than two firearms is punishable by up to one year in county jail or a state prison term of 16 months, two years, or three years.14California Legislative Information. California Code Penal Code PEN 30605 – Possession of Assault Weapon
- Manufacturing or distributing an assault weapon: four, six, or eight years in state prison, with a consecutive one-year enhancement for selling or giving one to a minor.15California Legislative Information. California Code PEN 30600 – Manufacture or Distribution of Assault Weapons
- Possessing a short-barreled rifle: up to one year in county jail or 16 months, two years, or three years in state prison.5California Legislative Information. California Code Penal Code 33215 – Restrictions Relating to Short-Barreled Rifle or Short-Barreled Shotgun
- Possessing a silencer: a felony carrying 16 months, two years, or three years in state prison, a fine up to $10,000, or both.6California Legislative Information. California Code PEN 33410 – Possession of Silencer
- Possessing a large-capacity magazine: an infraction with a $100-per-magazine fine, or a misdemeanor with up to one year in county jail and fines.7California Legislative Information. California Code PEN 32310 – Large-Capacity Magazine
A felony conviction also means permanent loss of your firearm rights in California. The offending firearm is confiscated. Multiple firearms in a single incident are charged as separate offenses, so the counts stack. The distance between a legal .300 Blackout build and a felony charge can come down to a single part, and law enforcement rarely gives the benefit of the doubt on configuration questions.