The Benelli M4 is the most expensive shotgun most people will ever consider, and the strange thing about upgrading one is how little it needs. Benelli lists the M4 Tactical with the pistol grip (#11707) and with the standard stock (#11703) at $2,299 MSRP, the H2O Titanium Cerakote versions at $2,399, and the new M4 EXT at $2,599. Every one of them ships with ghost-ring sights, a receiver Picatinny rail, an 18.5-inch barrel with a screw-in choke, and the gas system that is the whole reason to buy the gun.

So this is not a top-ten list. Gear Guy's M4 catalog is nine parts, eight of them factory Benelli, and that is roughly the honest size of the upgrade conversation. What follows is what is worth doing, what is mostly paperwork, and what to leave alone.

WHAT YOU ARE PAYING FOR: THE ARGO SYSTEM

Benelli's Auto-Regulating Gas-Operated system, ARGO, is a piston-driven design that Benelli says was designed for and approved by the U.S. Marine Corps. It runs on dual short-stroke gas pistons that Benelli describes as self-cleaning and as needing no tuning. Compare that with an inertia gun, which depends on the gun's own recoil to cycle and can get finicky when you add weight to it, or with a conventional gas gun that has a long-stroke piston and a valve to adjust. The ARGO system is the reason the M4 keeps cycling after a light, a side-saddle and a full tube have been hung on it.

The upgrade advice that follows from this is short: do not touch the gas system. There is no aftermarket piston, spring or tune that makes an M4 run better than Benelli shipped it, and the parts you add elsewhere on the gun are the ones that count under federal law.

THE STOCK AND THE TUBE

This is the M4 upgrade that has generated more forum threads than every other combined, and it is worth understanding rather than just buying.

THREE FACTORY STOCKS

THE 7+1 TUBE

Civilian M4 Tactical models ship 5+1. The full-length 7+1 tube is factory on the EXT and on the law-enforcement models, and Benelli's own 70052 seven-round tube is sold as a part; Midwest Gun Works lists it at $89, again as a restricted item, and notes that gunsmithing is required for installation. Aftermarket full-length tubes exist too. The catalog carries both factory tubes, the 5+1 and the 7+1, so you can see what the full-length tube does to the profile before deciding.

THE 922(r) PART

Here is why the stock and the tube are treated differently from every other upgrade. The M4 is an imported shotgun. Federal regulation 27 CFR 478.39 prohibits configuring a semiautomatic rifle or any shotgun with more than 10 imported parts from a list of 20 if the result would be a firearm that could not be imported as a sporting arm. The list includes buttstocks, pistol grips, forearms, magazine bodies, followers and gas pistons, which are exactly the parts in play when you add a collapsible stock and a full-length tube. It is the reason the aftermarket sells U.S.-made versions of both parts, and the background to the years when the collapsible stock and the seven-round tube were law-enforcement items on the civilian M4.

This article is not going to count parts for you. Verify compliance before you change the configuration, and keep the receipts and the country of origin for every part you add. Two things make it simpler than it used to be. First, Benelli now states that the M4 EXT is 922R compliant as shipped, with the 7+1 tube and the 5-position stock on it from the factory. Second, the arithmetic favors the EXT: an #11707 at $2,299 plus the factory stock at $325 and the factory tube at $89 comes to $2,713 before any compliance parts or gunsmithing, against $2,599 for the EXT. If you have not bought the gun yet and you want both features, buy the one that ships with them. These are federal rules only; magazine capacity and collapsible stocks are also state questions, so verify your state law.

SIGHTS

The M4's factory sights are an adjustable rear ghost ring and a windage-adjustable front sight, and on a $2,299 shotgun they are not the weak point. There is no aftermarket sight in the catalog, and none is recommended here. If the front sight is hard to pick up at night, that is a lighting problem, not a sight problem, which is what the next two sections are about.

OPTIC MOUNTS

The M4 comes with an integrated Picatinny rail on the receiver, which Benelli describes as being there for a light or optics. That means a red dot needs a mount, not a plate, and the mount's height decides whether you can still see the ghost ring through the window. Lower is better for a co-witness; higher is better for shooters in a gas mask or with a very short length of pull. Weight is the hidden cost. Benelli lists the M4 at 7.8 pounds bare, and everything you put on the rail sits high and forward of the shooter's hands. Gear Guy's M4 catalog does not yet carry a named optic mount we have verified, so there is no recommendation until it does.

LIGHTS

The factory forend is smooth polymer with no M-LOK, and the receiver rail is the wrong place for a light on a shotgun. That leaves an aftermarket forend with slots, or a clamp on the barrel or tube. The catalog carries an M-LOK forend so you can see what a slotted forend does to the gun's profile, but it is an unbranded representative silhouette, not a product, and it is labeled that way in the app. We are not naming a forend or a light for the M4 until we can verify one. When you shop, check that the forend is made for the M4 specifically: its gas system sits under the forend, which is why forends from other shotguns do not cross over.

SIDE-SADDLE

An on-gun shell carrier is the one upgrade that costs nothing in reliability and is worth doing on any defensive shotgun. On the M4 the receiver is anodized and the carrier has to clear the bolt handle, and on the EXT the oversized bolt release, so it is a fit question rather than a generic purchase. There is no side-saddle in the M4 catalog yet and none is named here. As with the Mossbergs, a velcro shell card is the cheap way to find out whether you want shells on the receiver at all before you drill or clamp anything.

WHAT IS NOT WORTH IT

Gas system parts, as above. Trigger work, because the M4's trigger is a duty trigger on a duty gun and the money buys more in a light. A different choke, unless you have patterned your defensive load and found a problem; the factory modified tube is a reasonable place to start. And a second stock if you already own the one you want. Most M4 owners end up with a light, a carrier and maybe a shorter stock, and that is the whole list.

ON THE BENCH IN GEAR GUY

Gear Guy renders the M4 in 3D from real named parts. The three factory stocks, the two magazine tubes, the factory forend and the ghost-ring sights are all on the bench, so the fixed-versus-telescoping and 5+1-versus-7+1 questions can be looked at side by side before any of them are bought. The compatibility engine warns on physical conflicts and suggests fixes, and a finished configuration shares as a link at gearguyapp.com/b/.

The gun itself lives in the Armory, an AES-256-GCM encrypted vault on the device with no account and serials masked by default, which is where the 922(r) receipts and part origins belong. The range log tracks round counts and deducts ammunition as you shoot, the Capability sheet shows whether the configuration carries a white light, Identify reads a photo of a shotgun and stands it up on the bench, and Premium users can export a PDF insurance and estate report of everything in the vault.

FINAL THOUGHTS

The M4 arrives finished. Buy a light and a way to mount it, add shells to the receiver, and shorten the stock if the fixed one is too long. If you want the collapsible stock and the seven-round tube, the M4 EXT is now the cheapest and simplest way to get them. Everything else is either paperwork or money that would do more somewhere else.