Self Defense

Mossberg 590RM

By: Dave Bahde

The most innovative pump shotgun ever produced?

One of the constraints/criticisms of shotguns (pump and semi) is their tube-style magazines. For anyone unwilling to spend many hours of practice, and possibly hundreds of dollars on accessories, they are slow and cumbersome to load and carry a limited capacity. This is one of the reasons that AK-based or similar shotguns are so popular amongst competitors. Swapping magazines is similar to their rifle and does not require an entirely new process. Along with that process, the capacity is dictated by barrel length — especially on defense guns. You want your defense shotgun, pump or semi, to be shorter, handier, and lighter. The solution, of course, is a box-magazine-fed pump gun, and while they have been around, Mossberg has taken this concept to an entirely different level. Not only are they making a 590 Tactical using a double-stack removable magazine, but they have now managed to alter the controls to operate similarly to the ubiquitous AR.

A detachable-magazine-fed pump-action defense shotgun will be the ideal configuration for some, and Mossberg has had the recipe dialed in since 2018. Available in 5, 10 (one included), 15, and 20 round versions, they insert via an AK-style “rock and lock” motion and detach via a steel AK-style paddle lever. While not inexpensive, these magazines are very robust and reliable.

Mossberg 590RM Magazine Fed 12 Gauge

In 2018, Mossberg launched their 590 magazine-fed shotgun. Using a purpose-built box magazine holding 10 rounds, it was a bit of a game-changer, and making it a double-stack eliminates the need for two-foot-long magazines. Like anything new, it took some time for the gun-buying public to warm up to it, but it received solid reviews and won over many people. It even convinced an agency or two to reintroduce the shotgun to their inventory. With 15- and 20-round magazines available, many competitors in “heavy” divisions requiring a pump gun also seemed to gravitate towards it. Use the optional five-round magazine, and it remains relatively short top to bottom. The addition of a box magazine was great for those accustomed to the typical shotgun controls, but many wanted more familiarity with AR-style rifles. Enter the new-for-2025 Mossberg 590R and 590RM.

Mossberg’s “R” series shotguns feature the new ambidextrous rotary-style safety selector mounted on the sides of the receiver, a familiar system to anyone accustomed to the AR platform. Other enhancements include the flat-faced trigger and easily accessible bolt release that rides in line with the top of the pistol grip. A Picatinny optic rail and (on this model) Magpul MBUS flip-up sights are standard equipment. We used Trijicon’s ultra-durable RCR red-dot optic throughout testing.

These new 590s added an AR-style five-position buttstock, an ambidextrous rotary safety in roughly the same position as an AR, a slide release that could be depressed without coming off the grip, Magpul MBUS flip-up sights, and a Picatinny optic rail atop the receiver. While the 590R uses a traditional tube magazine, the 590RM accepts a detachable magazine. While the 10-round magazine is wider than the shotgun itself, it’s roughly the same length as a 30-round AR magazine. Operating controls are as close as it gets to an AR on a pump shotgun, and a flat trigger is added for those who prefer it, like me. QD sling swivel cups are added to the stock with M-Lok slots at the front for sling mounts, lights, or other accessories. The barrel measures 18.5 inches long and is equipped with an integrated heat shield. My test shotgun included a Trijicon (www.trijicon.com) RCR enclosed emitter red-dot sight. The RCR is likely the best tactical shotgun RDS available; it’s simple, rugged, clear, and built to withstand most any condition. One 10-round magazine is provided, and a second was ordered up from Mossberg to practice magazine changes.

The 590RM’s phosphate-coated 18.50-inch barrel wears a heat shield, a Picatinny front sight platform, and an M-LOK adapter, which we used to attach a QD sling swivel mount on one side and a SureFire Micro Scout Light Pro weaponlight on the other.

Range Time

After some function testing at home, this 590RM went with me to Gunsite Academy for a different event, allowing me to run it at my favorite range — the multi-quad. Multi-quad is a nearly 360-degree range with multiple vehicles present, and is used during several of our more advanced classes. The setting is ideal for a tactical shotgun, as you are likely to be closer in and have to work in and around vehicles or obstacles.

One of the major differences with this type of shotgun is the lack of stock “cast”, as they are generally straight back from the receiver, like an AR. While cast is critical on a competition shotgun, straight back has its advantages for some with a tactical shotgun. Felt recoil tends to be less, and recoil drives the shotgun straight back into your shoulder, creating less muzzle rise. With a firm grip, it was possible to keep doubles on target more easily. Being able to adjust the length of pull without needing to remove the stock to shim it is a huge advantage to me with the 590RM’s adjustable stock. Sighting in the Trijicon RCR was relatively easy, and the BUIS were pretty close from the factory. For those instances where slugs are in order, this shotgun could be dialed in tight. The rotary safety is easy to access, but the slide release requires lifting a lever on the left side of the pistol grip, which took me a bit to get used to. But once I was dialed in, it was pretty fast.

A five-position adjustable buttstock allows precise fitment to the shooter, while its monster of a recoil pad takes the punishment out of firing full-boat buckshot and slugs. With a total of five QD receptacles out back — one on either side of the receiver extension and three on the buttstock — finding the right spot to plug in a sling is a non-issue. Magpul’s excellent rubber-coated MOE+ handles handgrip duty.

Most of my testing was completed using Federal Top Gun and some of their other competition loads. Patterning was completed using Federal Tactical LE127 00 buckshot. As usual, the LE127 stayed inside the diameter of my fist out to 20 yards with one flyer, sometimes two. Anything closer and it was mostly a single big hole; at 10 yards, it barely left the diameter of the wad. Function was flawless, and the straight stock helped make cycling fast. The recoil pad is a monster, but it kept even the higher-velocity stuff pretty comfy, and with the practice loads, it was downright soft. Having run Remington 870s and Mossberg 590s with standard controls for a long time now, it took me a few sessions to get used to the 590RM’s control placement/function, but once acclimated, it was fast, fun to run, and well-suited to defense or LE work.

The magazine is, well, big, but not cumbersome. The more I used the ten-round magazine, the more it started to go unnoticed — until you wrap your hand around it. With experience running a Desert Tech Quatro 53 AR-15 lower/magazine, it’s very similar in dimensions. Magazine pouches need to be changed, but it did fit in my pants pocket, which is my normal placement these days. Inserting is a rock and lock, ala AK, so not a big switch for me, but a switch for some. I also found myself altering my process a bit, keeping the slide open during the reload, then closing it as I move back onto target. That saved some time, made the reload smoother and faster, and tended to work well.

Using Federal Tactical LE127 00 buckshot, at 20 yards, the 590RM consistently put the shot pattern into a fist-sized group. Get any closer, and you basically end up with one large hole.

Bottom Line

All said and done, the 590RM proved to be a great shotgun with some distinct benefits. For a long-time shotgun user, the controls and the use of a detachable magazine represent a learning curve, but it’s short. Given the similarities to an AR-style rifle, the transition back and forth will be easier for some, but the magazine is truly a game-changer for most. Magazines are big and bulletproof, but at over $100.00 a pop, they are also expensive. For those of us using AK-style shotguns, we’re used to expensive magazines, but it might be a shock for others. Most shotgun encounters are over in ten or less rounds, but the ability to reload your payload all at once is really kinda nice. The 590RM is one of the most innovative pump shotguns ever introduced, and should be a very strong consideration for anyone looking at conventional tube-magazine versions. See it at your nearest dealer, or for more information, contact Mossberg; Tel.: (203) 230-5300; Web: www.mossberg.com.