Mossberg Optic-Ready 940 Pro Tactical 12-Gauge Shotgun: Full Review

Reflex optics are now commonplace on carbines and pistols, but not so much for defensive shotguns. Mossberg’s 940 Pro Tactical may change that. It appears to be the first factory shotgun featuring a receiver that is cut for mounting optics.

The receiver is pre-cut, drilled and tapped to accept mini-compact reflex sights. The footprint accepts a short list of micro-optics that include the Shield RMSc ($500, shieldpsd.com) and SIG Sauer RomeoZero ($169, sigsauer.com). As with the Mossberg OR-model pistols, a cover plate is provided with the 940 Pro Tactical if you choose to run the shotgun without an optic. Because there are slight variations among red dots using the RMSc pattern, Mossberg also includes additional screws with each gun.

When mounted, the receiver cut was designed so that the reflex sight matches the width of the receiver. These shotguns also allow users to mount a Picatinny rail if one is preferred.

A shotgun with such a focus on micro red-dot compatibility is somewhat of a new concept (we know some custom gunsmiths have mounted them before), but the Mossberg 940 — Guns & Ammo’s 2021 Shotgun of the Year — was an evolutionary step forward in semiautomatic shotguns.

The Mossberg 930 series that preceded it was a durable and reasonably reliable gun, but it remained largely unchanged since it was introduced in 2005. The 930 was due for an upgrade.

The 940 featured a new gas-operating system that was easier to maintain and even more reliable than the 930’s. Functionally, the 930’s and 940’s gas systems operate similarly. There are two vent holes drilled into the barrel lug that funnel gas into an operating system that uses the energy from those gases to cycle the action. The 940 models now come with a piston with stainless-steel gas rings. (Think of an AR-15’s gas rings.) As gasses move into the system, the piston is forced back into the spacer tube that surrounds the magazine and the spacer tube then exerts rearward pressure on the so-called “pusher.” Integral to the pusher are two metal rods that force the bolt to unlock and move rearward. Upon firing, and as the bolt starts to unlock and move, a spent shell is extracted from the chamber, which is then ejected. A tail on the bolt compresses a mainspring in the stock. As gas pressure is reduced, and after the empty shell is ejected from the action, the bolt is then driven forward. During the bolt’s forward progression, a new shell is picked up from the carrier and chambered. Hence, the gun is back in battery.

The major difference between the 930 and 940 systems is that the piston and magazine tube in the 940 are nickel-boron coated. This treatment resists fouling better and makes the 940 go longer between cleanings. Additionally, the spacer tube on the 940 is corrugated with ports along its length. The corrugation creates slots between the spacer tube and the magazine tube. This allows the gun to run properly by reducing the contact area between the spacer and the mag tube, even if there is substantial fouling. The holes in the tube also create a channel that allows fouling to escape.

Mossberg recommended cleaning the 930 every 500 rounds. Improvements to the gas operating system on the 940 allows users to forgo cleaning for 1,500 rounds.

The metal surfaces within the gas system, and the hammer and sear, also feature nickel-boron coating. Debris is much easier to wipe clean.

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Designing a reliable semiautomatic shotgun is a challenge due to the inherent variation among shotshells. The same gun that is expected to run light 2¾-inch, 1-ounce target loads is also expected to run 3-inch magnums. However, there is a significant difference in gas pressures. The 940 was given a versatile gas system that compensates for these varying pressures. In the case of the 940, excess gas from heavy loads is simply vented through ports in the barrel lug, which moderates bolt speed.

“Twelve-gauge shotguns have to be able to run light loads without beating themselves to death,” John Raciti, senior project engineer at O.F. Mossberg & Sons, told G&A editors. “A slow bolt is a happy bolt.”

Raciti and his team at Mossberg used slow-motion cameras to determine bolt speed and adjusted the gas system was necessary to meet the goals of the 940. Since bolt speed is predicated by a variety of factors (including the diameter of the gas ports and the weight of the piston), the engineers had to design a system that worked with both light and heavy loads.

Raciti’s team found that the 940 Pro Tactical surpassed the 1,500-round recommended limit without cleaning. However, the fouling inside the gun made them more difficult to disassemble and wipe down. Cleaning the gun before it reaches 1,500 rounds makes the process easier.

Another subtle upgrade to the 940 Pro Tactical is a trimmed forend. This is a nice touch on field guns, but on defensive and competition shotguns, the trim forend simplifies quad-loading the magazine tube. It also makes the gun more streamlined and comfortable to handle.

Stock spacers included with the 940 Pro Tactical allow us to adjust length of pull from 12½ to 14¼ inches. This is particularly important on law enforcement and defensive shotguns because it allows the shooter to modify the gun to the situation. This is especially true for law enforcement professionals who wear vests. Also included with the 940 are shims for adjusting the drop of the stock and cast.

With its 18½-inch barrel, the 940 Pro Tactical has a maximum overall length of 37½ inches. Unlike most defensive shotguns, the 940 Pro Tactical features removable chokes. One Cylinder AccuChoke tube is included, but having the ability to swap chokes makes this gun much more versatile. The barrel is flared at the muzzle, too, which gives the shotgun a beefier profile, but also makes it possible to view the fiber optic front sight — even when some red-dot sights are mounted.

Magazine capacity is 7 rounds, up from the standard 4 rounds, thanks to the included extension tube. A bright orange-anodized aluminum follower sits inside to alert you to the status of ammo on board.

Like most tactical semiauto shotguns made these days, the Mossberg 940 Pro Tactical has oversized controls. The bolt handle is large, knurled and cylindrical. The bolt release is a pronounced lever-style design that’s easy to slap when performing reloads from a bolt-lock condition.

As with other Mossberg shotguns, the safety selector is positioned on the tang, and it must be pressed forward to fire. There’s nothing oversized about the safety switch though; it’s typical Mossberg.

The trigger fires after 4½ to 5½ pounds of pressure is applied. The trigger feel is far better than triggers on many other defense-minded shotguns. The 940 Pro Tactical’s black polymer stock keeps gun weight to around 7½ pounds, and the polymer construction makes the stock robust and durable.

With an MSRP of $1,120, this Mossberg shotgun isn’t “cheap.” However, when you consider the gun’s build quality and long list of standard features, the 940 Pro Tactical seems like a bargain when sitting next to a Benelli M4 that costs almost twice as much. However, Stoeger’s M3000 Defense shotgun carries a starting MSRP of $559.

At the Range

Gas-operated shotguns like the 940 Pro Tactical allow you to quickly run slug selection drills with a semiauto shotgun. With the 940, this simply requires inserting a slug into the magazine tube, pulling back on the bolt handle to chamber the slug and firing. With a full magazine, you have to either fire or cycle the gun to make space in the magazine before inserting the slug into the tube.

The Mossberg’s enlarged and beveled loading port and elongated carrier made it easy to load this gun quickly. That’s a byproduct of input from Mossberg pro shooters includ-ing Jerry Miculek who assisted in the design of the 940. The new loading port/carrier is beneficial even to those who don’t shoot competition. The effort also prevented pinched thumbs.

G&A fired more than 100 rounds of magnum ammunition, and the 940 wasn’t too abusive. Even when shooting from a bench to zero the gun at 50 yards with slugs, it was manageable. Accuracy and performance are enhanced by one of the best triggers in any tactical shotgun. Perhaps the most important feature is the machined receiver that allows for the addition of a reflex sight.

The 940 Pro Tactical begs the question why all shotguns shouldn’t come equipped with a slide cut to accommodate reflex sights. It would alleviate sighting issues for cross-dominant shotgun shooters. This 940 is a practical and intelligent step forward in the design of semiauto shotguns.