A collapsible stock on a Benelli M4 is not legal in California if the shotgun also has a pistol grip, which the standard tactical M4 does. That combination — a semi-automatic action, a protruding pistol grip, and a folding or telescoping stock — meets the state’s definition of an assault weapon under Penal Code 30515. No permit, registration, or workaround changes that outcome. The only lawful path is modifying the shotgun so one of those features is gone.1California Legislative Information. California Code PEN 30515 – Assault Weapons
Why the Stock and Grip Together Trigger the Assault Weapon Law
California uses a feature-based test for semi-automatic shotguns. Under Penal Code 30515, a semi-auto shotgun becomes an assault weapon if it has both a folding or telescoping stock and a pistol grip that protrudes conspicuously beneath the action (a thumbhole stock or vertical handgrip counts the same way).1California Legislative Information. California Code PEN 30515 – Assault Weapons
Neither feature alone is prohibited. A semi-auto shotgun with a collapsible stock and no pistol grip is fine. A semi-auto with a pistol grip and a fixed stock is also fine. The statute only reaches the gun when both features appear together.
The standard Benelli M4 tactical model ships with a pistol grip built into the stock and, on many variants, a telescoping stock that slides shorter or longer with a button or lever. That factory configuration is exactly what the statute describes. To keep the shotgun in California, you have to remove one side of the equation.
Making the Stock “Fixed” So the Pistol Grip Can Stay
Most M4 owners keep the pistol grip and neutralize the stock, because the grip is central to how the gun handles. California’s regulations define a fixed stock as one that “does not move, fold, or telescope,” and a telescoping stock as one “shortened or lengthened by allowing one section to telescope into another portion.”2State of California – Department of Justice – Office of the Attorney General. California Code of Regulations Title 11, Division 5 – Assault Weapons Identification If it moves at all, it isn’t fixed.
The standard fix is pinning. A roll pin or hardened fastener is driven through the stock’s adjustment mechanism so the sliding portion cannot move. The pin has to be robust. If someone can press a button, pull a lever, or yank the stock to a different position without a tool, the stock is still telescoping under California law, and the shotgun is still an assault weapon.
The workable standard: changing the stock length must require disassembling part of the firearm or using a dedicated tool such as a punch or screwdriver. A properly pinned stock passes because you would need to drive the pin out first. Some manufacturers sell M4-compatible replacement stocks that arrive pre-pinned at a specific length of pull. If you go that route, confirm the pin cannot be removed by hand and is not a friction fit that could work loose. A pin that loosens over time carries the same legal consequences as never installing one.
The Other Option: Losing the Pistol Grip
You can instead run a telescoping stock legally if the gun has no pistol grip, thumbhole stock, or vertical handgrip. In practice, this means a field-style stock design where the wrist of the stock does not protrude conspicuously beneath the action. This route is less common on the M4 because it changes the ergonomics the shotgun was built around, and because the pistol grip is molded into most factory M4 stock assemblies rather than existing as a bolt-on part. For most owners, pinning the stock is the cleaner modification.
Penalties for Running the Prohibited Configuration
Possessing a shotgun that meets the assault weapon definition is a criminal offense under Penal Code 30605. The charge is a wobbler. As a misdemeanor it carries up to a year in county jail; as a felony, 16 months, two years, or three years in county jail under California’s realignment framework.3California Legislative Information. California Code PEN 30605 – Unlawful Acts Relating to Assault Weapons and 50 BMG Rifles
The exposure is higher if a prosecutor treats the swap itself as manufacturing. Penal Code 30600 makes it a straight felony to manufacture, distribute, transport, or import an assault weapon into California, with a sentencing range of four, six, or eight years.4California Legislative Information. California Code PEN 30600 Someone who buys a compliant M4 and then installs a collapsible stock could face that charge rather than simple possession.
Registration is not an option. California’s assault weapon registration windows closed years ago, and no current process lets you keep a prohibited configuration on the books.5State of California – Department of Justice – Office of the Attorney General. Frequently Asked Questions – Registered Assault Weapons If your M4 has both a pistol grip and a collapsible stock today, the choices are modification or surrender.
Federal Rules That Also Apply When You Modify
The M4 is manufactured in Italy, and swapping parts on an imported semi-automatic shotgun can trigger 18 U.S.C. 922(r). The implementing regulation caps the number of designated foreign-made parts in a non-sporting configuration at ten of twenty listed components.6Office of the Law Revision Counsel. 18 U.S. Code 922 – Unlawful Acts Replacing the factory stock with a U.S.-made fixed stock counts as one of your substitutions. Keep records of which parts you have replaced and where they were made; the burden of showing compliance is on the owner.
Length is a separate federal concern. Under the National Firearms Act, a shotgun with a barrel under 18 inches or an overall length under 26 inches is a short-barreled shotgun requiring registration and a $200 tax stamp.7Bureau of Alcohol, Tobacco, Firearms and Explosives. National Firearms Act California separately prohibits short-barreled shotguns under Penal Code 33215. Overall length is measured from the muzzle to the rearmost point of the gun, along a line parallel to the bore.8Bureau of Alcohol, Tobacco, Firearms and Explosives. National Firearms Act Handbook With a standard 18.5-inch barrel, a factory M4 with the stock collapsed usually still clears 26 inches, but if you pin the stock shorter than the factory collapsed position, measure before you finish the job. An NFA violation carries up to ten years in federal prison, which is a much larger problem than the assault weapon classification you were trying to fix.
A California-Legal Benelli M4 Checklist
- Stock permanently fixed (pinned so it cannot telescope without a tool) if the shotgun has a pistol grip.
- Or a telescoping stock only if the shotgun has no pistol grip, thumbhole stock, or vertical handgrip.
- Overall length of at least 26 inches with a barrel of at least 18 inches.
- If parts have been replaced, no more than ten of the twenty designated 922(r) components are foreign-made.
The lowest-risk approach is buying a factory California-compliant M4 with a pre-pinned stock. If you are modifying a shotgun you already own, have a qualified gunsmith do the pinning and verify overall length after the work. Keep documentation of every part changed, including manufacturer and country of origin. If the configuration is ever questioned, that paper trail is what separates a short conversation from a felony investigation.