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Mossberg 590A1 M-LOK Shotgun Review

Mossberg's new 590A1 M-LOK embodies many of the features that make a pump-action shotgun the right choice for defense.

Mossberg 590A1 M-LOK Shotgun Review

Mossberg 590A1 M-LOK pump-action shotgun (Michael Anschuetz photo)

Mossberg’s 590A1 shotgun is built for hard use. Featuring mil-spec construction, according to Mossberg, the 590A1 is the only pump-action shotgun to pass Mil-Spec 3443E and has been selected for duty by the U.S. Armed Forces. Select models feature Parkerized and Marinecote finishes; fixed, full-length, six-position adjustable, +4 Shell Holder, and Magpul buttstocks; and XS rail-mounted sights. The model I selected for this review features the Parkerized finish, a Ghost Ring adjustable rear sight, and a special M-LOK forearm. I’ll get into the details of those features in a minute, but first, let’s review some of the reasons a pump shotgun is a good choice for defense.

Almost every review you read about tactical shotguns talks about their versatility. That’s certainly true when you’re talking about the different types of ammunition that can be used in a tactical shotgun. For example, there are buckshot loads, slug loads, and specialty loads that really do fit a wide range of applications.

Other reasons cited by shooters always include testimonials about the utter reliability of a pump shotgun. According to more than one forensic technician, pump-action law enforcement shotguns rarely, if ever, malfunction.

A pump-action shotgun with an 18.5- to 20-inch barrel is easy to handle in confined spaces, and it stores pretty easily even in a vehicle. Many of them weigh enough that felt recoil is manageable, but they aren’t so heavy that a defender with a slight build cannot shoot them comfortably.

And I would be remiss if I didn’t mention the pop-culture phenom centered on the pump gun’s intimidating sound when the action is worked. More than one lawman has referred to that as being one of the most “ominous” sounds a criminal can hear.

Mossberg 590A1 M-LOK shotgun
The new Mossberg 590A1 M-LOK features a red-stripe front sight that’s dovetailed into a two-tier ramped base. Both tiers have horizontal striations to reduce glare. (Michael Anschuetz photo)

590A1 M-LOK Features

The 12-gauge 590A1 M-LOK has several key features. Starting at the muzzle end, the first feature you notice is the tall front sight with a bright red stripe running vertically up the blade. The blade is dovetailed into the two-tier ramped base, and both tiers have glare-reducing horizontal striations. The barrel has a screw-in choke that is rated Cylinder Bore. I checked it with my choke tube gauge, and sure enough, the Cylinder Bore gauge dropped right in. The barrel is 18.5 inches long with a 3-inch chamber, so it accepts 2¾-inch and 3-inch shells.

The magazine tube with the cap in place is almost as long as the barrel (it’s only about 1 inch shorter), and it holds six rounds. The end of the metal magazine tube cap has a sling-swivel stud.

The gun’s forearm is black synthetic, and it has seven planes going around its circumference. Five of those planes have rows of M-LOK slots. Three rows have five slots (three that are 1.27 inches long and two that are 0.65 inch long), and two rows have four slots (each is 1.27 inches long). The forearm is 8 inches long and 1.76 inches in diameter.

The receiver of the 590A1 is drilled and tapped, and as I said earlier, my version has an adjustable Ghost Ring rear sight. The sight is surrounded by a heavy-duty protector (the steel is 0.09 inch thick). The sight is fully adjustable for windage and elevation, and it’s secured to the receiver by two stout hex-head screws.

Mossberg 590A1 M-LOK shotgun
Mossberg 590A1 M-LOK (Michael Anschuetz photo)

The Mossberg 590 action has a fine reputation for reliability and durability. Based on the well-known Model 500 pump-action platform, the 590A1 features non-binding twin action bars, positive steel-to-steel lockup, an anti-jam elevator, dual extractors, a drilled-and-tapped receiver, and an ambidextrous top-mounted safety. It also has a convenient clean-out magazine tube for ease of maintenance.

The action lock lever is located on the left side, slightly rearward of the metal trigger guard. Speaking of the trigger guard, it’s nice and large and will accommodate a gloved trigger finger. The two-position safety is located on top of the receiver and is positioned for easy access. The safety button is also metal.

The trigger pull on my sample averaged 7.5 pounds, according to 10 measurements with my RCBS trigger pull scale. There’s a noticeable amount of take-up, but it breaks crisply and consistently. The trigger mechanism has a trigger-adjustment screw that can be accessed by removing the gun’s trigger assembly from the receiver.

Here’s how you do it. Move the safety fully rearward to the “On” position (a red dot shows when the gun is in firing mode). Check the chamber, elevator, and magazine tube to be certain the gun is unloaded. Note that Mossberg recommends wearing eye protection during disassembly and cleaning. Depress the action lock lever located on the left-hand side of the receiver and open the action by sliding the forearm fully rearward. Then move the forearm forward until the bolt is positioned halfway open in the middle of the ejection port. Unscrew the magazine tube cap (it turns counterclockwise). Take caution because the magazine spring retainer and spring are under pressure. Remove the barrel from the receiver.

Mossberg 590A1 M-LOK shotgun
The most distinguishing feature of the review sample is the M-LOK-slotted forearm. It makes attaching a variety of lights, lasers, and accessories very easy. (Michael Anschuetz photo)

With the barrel removed, place the receiver on a stable surface with the trigger guard up. Using a punch 3/16 inch or less in diameter push out the small trigger housing retainer pin located on the side of the receiver. Then remove the trigger housing by lifting the rear portion first. Do not disassemble the trigger assembly and do not squeeze the trigger when the trigger housing is removed from the receiver.

The trigger pull can be adjusted by rotating the hex-head trigger-pull-adjustment screw located in the rear of the trigger housing. Turning the screw clockwise increases the trigger pull and rotating it counterclockwise decreases the trigger pull. Mossberg cautions users to not remove the trigger-pull-adjustment screw. The minimum trigger pull setting is with the screw flush with the bottom surface of the counterbore in the trigger housing. Reassemble the gun before testing the trigger.

My 590A1 M-LOK’s fixed buttstock is black synthetic with a very slight pebbled texture. The texture is not exactly smooth, but it’s not very aggressive, either. There is a sling-swivel stud in the typical location, and the butt has an effective 0.75-inch-thick recoil pad. Length of pull is 13.87 inches. Overall length is 39.5 inches. And unloaded weight of the 590A1 M-LOK is 7 pounds.

Mossberg 590A1 M-LOK shotgun
The 590A1 M-LOK’s rear sight is a fully adjustable Ghost Ring type, and it is protected by a sturdy, 0.09-inch-thick steel guard that surrounds it. (Michael Anschuetz photo)

590A1 M-LOK Specs

MANUFACTURER: O.F. Mossberg & Sons;
TYPE: Pump-action shotgun
GAUGE: 12; 3-in. chamber, Cylinder Bore choke
BARREL: 18.5 in.
STOCK: Synthetic; M-LOK forearm, 0.75-in. recoil pad
LENGTH OF PULL: 13.87 in.
FINISH: Parkerized barrel and action, black stock
SIGHTS: Adjustable Ghost Ring rear, red-stripe front
SAFETY: Two position
TRIGGER: 7.5-lb. pull (as tested)
MSRP: $690

Mossberg 590A1 M-LOK shotgun
The two-position safety is conveniently located on top of the receiver, and its button is made of metal. The test gun’s safety was fast and easy to operate. (Michael Anschuetz photo)

The 590A1 at the Range

The first thing I did was pattern the 590A1 M-LOK at 15 yards using Hornady TAP buckshot, Federal Personal Defense 00 Buckshot, and Federal 1-ounce slug loads. I also tried Federal’s new Force X2 buckshot loads, and you can read about them in my Quick Shot report elsewhere in this magazine. Shooting on plain brown paper, the gun put shot charges on point, and the Cylinder Bore choke kept the pellets of buckshot in a 10-inch radius at that distance.

Taking a cue from fellow Shooting Times writer Steve Gash, who recently wrote about the defensive shotgun training course he attended at Gunsite, I set up some different drills at various ranges, shooting at a variety of targets—some were steel plates of different sizes, some were paper silhouette targets. Starting at 15 yards, I fired first one round, then two, then three more. Then I reloaded as quickly as I could and fired two more rounds. Then I moved back to 20 yards and repeated that whole routine.

After shooting at those two distances, I tried some of the rifled slugs. Shooting from the bench, the gun put three slugs into groups ranging from 3.0 to 4.0 inches at 25 yards. I also fired a full magazine (six rounds) of slugs, three from a sitting position and then three from standing, and I put them all into the man-sized silhouette. The sights made aiming fast and easy.


Just for the heck of it, I moved back to 50 yards and tried my hand with the slugs on a large steel target. Although I didn’t hit the plate every time, I did much better than I thought I would, which is a testament to how good the 590A1 shoots. At a close self-defense distance of seven yards, the gun put six slugs into one big, ragged hole.

The gun fed, chambered, extracted, and ejected all shotshells and slug loads I tried without a hitch. The front sight was quick to pick up and easy to get on target in lower light situations, thanks to the bright red stripe. The day I did my shooting, it was cloudy and overcast, and I didn’t have any trouble picking up the front sight. It’s not visible in total darkness, but I could see it fairly easily inside in a dim hallway when our night light was turned on. The fact that the forearm is M-LOK slotted makes installing a weapon light or laser very easy in the advent that the shooter wants to equip it with such accessories. The two-position safety was fast and easy to operate, thanks to its prime location on top of the receiver. Pumping the action was smooth and efficient, and fired cases were ejected cleanly.

All that shooting just confirmed what I had discovered many years ago. A shotgun can be a very effective fight-stopper. With the right ammunition, it is not only tremendously effective up close, but it also is surprisingly accurate at reasonable distances. Of course, it may not be the best firearm for places where the risk of over-penetration through perhaps several thicknesses of drywall could possibly injure innocent bystanders. But for many applications it is the right fight-stopper.

Mossberg designed the 590A1 for military and law enforcement use, and its superb handling qualities also make it great for civilians. If you’re looking for a shotgun that has it all for protection of your family and your home, check out the dependable, rugged, and reasonably priced guns from Mossberg.

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