Mossberg's New 590RM Shotgun: Reviewed

The 21st century is turning out to be great!

October 02, 2025 By Patrick Sweeney

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When it looks like things might get noisy, and there is no way to leave the area, the first firearm I’m likely to reach for is a shotgun. Opinions vary, but if I have to dish out the penalty for putting my life and limb at serious risk, an ounce of plumbous payload often works wonders. The only problem is that once the five or eight rounds in the smoothbore are dispensed, reloading can take an achingly long time. Well, Mossberg has an answer. Two answers, actually.The Mossberg 590R is their new pistol-gripped shotgun with a rotary safety lever. The one I tested is the 590RM, with the rotary safety lever and a box magazine on the bottom, one holding ten rounds. Safety first.

Most shotguns use a safety that was not new when the first Roosevelt was President. That is, a cross-button that you push over. It blocks movement of the trigger, and it works one way. So, if you are a left-handed shooter, the safety works “wrong” for you. Mossberg took care of that back in 1961 with the introduction of their amazing new shotgun, the Model 500. It not only had an aluminum receiver (unheard of!), but the top-mounted safety meant two things: it worked just fine for both right and left-handed shooters, and of equal importance, you could see if it was on or off. With the cross-button safety, you have to either rotate the shotgun to look, or fumble around with a fingertip and feel if it is on or off. Neither is entirely satisfactory, and it was only because there was no other choice that we all got accustomed to it. Well, no more, post-1961.

The new rotary safety is mounted on the side of the receiver, and it, well, rotates to select safe or fire. It is ambi, that is, it exists on both sides of the receiver. The receiver is a modified Model 500 (which has itself changed little in the ensuing six decades) with a pistol grip and an adjustable stock. Both of those required other mods as well. The pistol grip incorporates the regular trigger housing of the Model 500 but modified to have a tab to bolt on an AR-15 pistol grip. If you don’t like the pistol grip the 590RM comes with (and I don’t, one of the few points of disagreement between me and Mossberg), then you simply take it off and replace it. The rotary safety is positioned above and just a bit forward of the pistol grip, in the perfect place for your thumb to actuate it.

Left and right side views — (top) The Mossberg 590RM offers both an ambi safety and a ten-shot box magazine. (bottom) The left side lacks an ejection port, but it has a safety lever. (Photo provided by author.)

The stock also required a change in the receiver. The 500 uses a regular stock, and the angle for the stock bolt means an angled back face. The 590RM stock extends directly back from the receiver, so Mossberg changed the back of the receiver to attach the stock and to provide lateral support for it as well. Oh, and the stock also incorporates QD sling swivel sockets, so you can sling your 590RM should you feel the need. The stock is adjustable for length of pull, and it also incorporates a recoil pad suitable for the force of a 12-gauge payload.

Stock fit to receiver — Here you can see the meeting of the stock and the receiver, and the modifications Mossberg had to make to the 590 design to fit the stock on. Well done, Mossberg. (Photo provided by author.)

The receiver of the 590RM also incorporates a Picatinny rail. Here, you can mount iron sights (the 590RM comes with them) or optics of some kind. The rail is only from the rear of the receiver where it meets the stock assembly, to just short of the front edge. It is not the full length of the barrel. The barrel is covered with a heat shield, an interesting addition, and a clear demonstration of the intent of Mossberg for the 590RM: defense. The rail and the barrel come ready for sights and the set included with the 590RM are Magpul. These are the MBUS 3, spring-loaded to pop up when you press the tab. So, you can have the 590RM racked or stored with the sights folded, and in a moment’s notice have them upright and ready for use. The rear is bolted to the receiver rail, while the front is clamped onto a base that is copper-brazed to the barrel. If you want something else, it is easy enough to dismount the Magpul sights and install something else, or go optics, since there’s a rail right there.

Front sight of shotgun — The front sight is clamped to a base that is copper brazed to the barrel. If you don’t like this Magpul, swap it for something else. (Photo provided by author.)

The barrel has an extension inside the receiver, one that the bolt locks to, so the receiver doesn’t take the forces of firing, just recoil. It is held on the same way as the Mossberg 590: with a cap that screws over the barrel hoop, the hoop riding over and around what would otherwise be the magazine tube. The barrel is threaded for screw-in choke tubes and the Mossberg pattern is so common that you can practically buy them at your corner gas station. (In some rural areas, that might actually be the truth.) The barrel hoop also incorporates an M-LOK slot on each side.

But the big news for the 590RM is the magazine. With additional modifications to the receiver, Mossberg found a way to secure a ten-shot magazine to the bottom of the receiver. They did this with three modifications. First, the front of the receiver, at what would otherwise be the magazine tube, they found a way to secure a front lug on the magazine in place. Next, they made further modifications to the trigger housing and put a magazine latch on there, complete with a big paddle to unlock it when you need to reload, and lastly, they put ribs on the magazine and corresponding slots on the receiver, to give the magazine support during recoil. Ten rounds of twelve gauge, hanging below the receiver creates a lot of leverage during twelve-gauge recoil. Without those slots, the magazine weight could make it rock, wear the locking shoulders, and then fall out. That would be bad, and Mossberg solved the potential problem.

The magazine is a solid assembly of various parts. The upper section with feed lips, the taper, and the main body, are all bolted together with the midsection, to create a magazine that could be used as an impromptu impact weapon if you ever run out of twelve-gauge ammo. There’s even a sliding baseplate that comes off to clean the magazine. Now, just in case you need a refresher, the 590RM is a pump-action shotgun. Derived from the 500 by way of the 590, it is not a self-loader. You still have to do the work of running the gun. Mossberg has redesigned the forearm, and it has lips front and back, as well as big ribs to afford a non-slip grip. This one should be on all pump shotguns.

Magazine release lever — The magazine catch is a big lever in back of the magazine itself. To reload, grab the magazine so you pinch the lever, and rock the mag. Also, note the magazine reinforcement ribs, inserted into the receiver slots. Good engineering, that. (Photo provided by author.)

Loading the magazine also takes a certain knack. It accepts 23⁄4-inch shells only. I suspect that try as the Mossberg engineers might, getting a magazine to accept and feed properly both 23⁄4- and three-inch shells proved impossible. I, for one, would not pass over a shotgun, the 590RM or any other, were it restricted only to 23⁄4-inch shells. I’m not sure I dislike anything enough to discharge ten three-inch shells of buckshot or slugs at it out of a pump shotgun. As the 590RM is clearly not a goose gun (the ten-shot magazines pretty much moves it out of that category), three-inch shells are not for me.

The feed lips are very short. To load, you have to use the round you are loading to press down the one already in the magazine. I found that when using skeet or trap loads, with their low-base metal, the extraction rim hit the front edge of the shell rim, and kept me from sliding it back,. I found that placing the magazine on the bench, and pressing the top shell down a bit with my left index fingertip gave me enough clearance to slide in the next shell with my right. High-brass shells did not pose the same problem.

I began the journey of three-gun and bowling pin shooting with a Mossberg 500, so I am familiar with how they work. The 590RM works just like the older ones, with one change: the pistol grip. The Magpul MOE has the high-and-back extra flange on the back of the pistol grip that a lot of shooters like. And I hate it. I find I much prefer to have my firing hand as high up on a pistol grip as I can get it, and the flange pushes my hand down, also changing the angle of my arm and elbow position, but that’s the beauty of the Mossberg approach. Since the pistol grip is bolted onto the trigger assembly, you can change it to whatever you want to.

The straight-line stock also changes the nature of the recoil. If you have spent you whole shooting life using a regular shotgun stock, the straight-back stock of the 590RM is going be different. Not bad, not worse, but different. The adjustable stock means you can change it to accommodate shooters of different heights. Me, of course, I run all such stocks all the way back, as I crawl a stock like there’s no tomorrow and if I don’t, I can end up with my nose on the receiver. In .223, that’s not a big deal. 12 gauge? You bet it would be.

Collapsable stock — The stock is adjustable for length of pull. It has a thick recoil pad on the back, and it is built to take 12-gauge recoil. (Photo provided by author.)

As far as performance, what can I say? Mossberg has made millions of Model 500 and Model 590s, they know how to make them reliable, and this one certainly was that. Back in the old days, we’d fuss over various buckshot and slug loads to find the one that that particular shotgun performed the best with. (Every shotgun seemed to be a law unto itself back then.) Today, we flip that on its head. Now you pick the load that delivers the performance you want, and then experiment with choke tubes until you get the pattern you desire. Me, I just used the choke tube that was in the 590RM when it arrived, and found it worked just fine.

As to reloading the 590RM, that was another new task to learn. In 3-Gun competition, the shotgun portions of a stage are the “who reloads fastest, wins” sections. On the 590RM, it was much more like reloading a battle rifle: reach up, grab magazine and tab, squeeze, rock and drop. Grab the next magazine, insert front, rock and lock. If you’ve ever worked an AK, FAL, M1A, G3 or the like, you know the drill.

Target showing pattern — Choose your buckshot and then adjust the choke tube to get the pattern you want. (Photo provided by author.)

So, should you run right out and buy a 590RM? The magazine is attractive. And if you have to have that, then the answer is simple. If you do not need a ten-shot box magazine, there is also an answer. The 590R is the same shotgun with rotary safety and all the other extras, but not the magazine. It is a regular feeds-from-the-tube pump shotgun, and you can have it that way if that is your preference. Mossberg, while pushing boundaries is very accommodating, God bless ‘em.