Mossberg 940 JM Pro 12-Ga. Semi-Automatic Shotgun Review

The Mossberg 940 JM Pro Shotgun Competes with the Top Semi-Autos Out There at a Third of the Price

The 102-year-old O.F. Mossberg company is known for its venerable pump-action shotguns. (The Model 500 alone has sold over 12 million units, likely making it the world’s most popular long gun, period.) But the “Mossberg makes good pumps” perception is changing. The perfect illustration of that is the Mossberg 940 JM Pro.

In 2020, the company unveiled an upgrade to its flagship semi-automatic, the model 930, but it didn’t just trot out the first model it could most quickly get to market. Rather, Mossberg led with the 940 JM Pro, a flashy race-car-of-a-shotgun designed by likely the best all-around shooter in history, Jerry Miculek.

It’s a shotgun conceived to compete with the best semi-autos available. And thanks to Mossberg’s well-oiled production line and sheer sales volume, the 940 JM Pro is priced significantly below others in its class. 

Inside the Mossberg 940 JM Pro 12-Ga. Semi-Automatic Shotgun

While the 940 has undergone a facelift, the real story is the overhaul on its internals that now run more efficiently with a wider range of ammo. How? The gas delivery system features two oversized ports in the cylinder. A dual short-stroke piston assembly accepts the burst of gas from the shell and slams rearward, moving the spacer tube, pusher assembly and the bolt rearward to cycle the action at similar speeds regardless of the load.

Another key to the 940’s enhanced reliability is owed to its innovative spacer tube. This aluminum cylinder that rides on the mag tube features grooves to reduce surface area and to allow carbon fouling and moisture from condensation a place to go rather than just building friction under it. All critical internal parts are boron-nitride-coated to further reduce friction. Translated, the 940 runs 1500 rounds without cleaning compared to 500 of the 930. 

Outside the Mossberg 940 JM Pro

Externally, the 940 has several key upgrades. Its plastic buttstock is adjustable via five spacers and shims that alter drop at comb/heel and cast on/off, as well as a modular buttpad system that makes the gun’s LOP adjustable from 13 inches to 14¼. This means it’ll even fit Jerry’s petite, champion-shooter daughter, Lena. These critical aspects of shotgun fit are imperative for intuitive shotgun shooting, recoil management and overall shooter satisfaction.

Next, engineers slimmed the fore-end and made it flush-fitting to the receiver, something Jerry insisted on to facilitate speed loading so the hand doesn’t snag. The JM Pro features an A 9-round extended mag tube below the gun’s 24-inch barrel. It comes with three (C, IC, M) premium Briley extended choke tubes that’d cost around $100 if you were to purchase them separately.

The 940 JM Pro features oversized controls to reduce fumbling. The bolt-release button also serves another nifty purpose. With the gate manually depressed, a push will release a shell from the magazine so the mag can be emptied — or a single shell replaced — without cycling each shell through the chamber. Its safety is wholly Mossberg and located on the tang. Its trigger averaged a superb 4 lbs. 12 oz. pull weight. 

Range Time

On the range, the 940 came up to my eye naturally; instantly I hit fast-flying targets without conscious thought, indicative of a gun that shoots where I look, thanks in large part to great stock fit and a well-regulated barrel. Furthermore, it’s silky to load, owing to its forend contour and non-pinching gate. The gun never jammed when shooting 11/8 oz. loads and heavier.

The 940 JM Pro delivered consistent patterns with Winchester AA No. 8s. Recoil was milder than expected from this lighter-than-expected 7 1/2-pound gun, thanks to its gas system, effective recoil pad, and impulse-soaking return spring. I’d deem the shotgun perfect if it had a modular cheek-pad system in its stock.  

In sum, the 940 JM Pro has everything you need to enter a 3-Gun competition right out of the box and still compete with guys shooting guns costing double. (And I’d pity the jackwagon who broke into your home not knowing you had this blue-yellow puppy fully stoked and waiting behind the door.) But for Mossberg it represents more than another good shotgun: Rather, it’s a shotgun that could change how the shooting public perceives Mossberg for the next century.

Specifications: Mossberg 940 JM Pro 12-Ga. Semi-Automatic Shotgun

• Type: gas-operated semi-automatic shotgun
• Gauge: 12, 3”
• Barrel Length: 24”
• Weight: 7 lbs., 7 ozs.
• Magazine Capacity: 9
• Stock: Synthetic; adjustable 13” – 141/4”
• Chokes: interchangeable Briley chokes: cylinder, improved cylinder, modified
• Sights: fiber-optic front Hi-Viz triangle bead
• Accessories: three choke-tubes and case, 5 shims, 4 spacers; multi-colored sight pipes, 3 butt pad spacers
• MSRP: Under $1100

This article originally published in June 2021.