Just about every shooter owns, has owned or will someday own a Mossberg Model 500 shotgun. Like a Winchester Model 94 or a Ruger 10/22, the old Mossy is just one of those guns that endures forever while newer designs come and go. It’s always been a snap to swap Mossberg 500 barrels, and now it’s literally a snap to swap out just about everything else. The Mossberg FLEX 500 is the most modular shotgun system ever made. It’s the Stoner 63 of pump-action shotguns. Is that cool or what? . . .
A few months ago, Mossberg sent me a basic FLEX 500 shotgun, then sent me all the pieces and parts you see here. No single shooter would ever need or particularly want all of these modular components, but Mossberg wanted to demonstrate the mind-blowing versatility of their new 500. Whether you want a riot gun, a goose gun or a slug gun, the FLEX has you covered.
The Venerable 500
If you’re not already familiar with the Mossberg Model 500, it’s time to get you acquainted. The venerable ‘Mossy’ is a pump-action shotgun that feeds from a 5-round tubular magazine. Its barrels are easily removed by unscrewing a captive knurled screw from the end of the magazine tube. Unlike the Remington Model 870, the Mossberg’s magazine capacity cannot be increased by installing an extended mag tube without also replacing the barrel.
The alloy receiver is not a stressed component. Instead of locking to the receiver, the bolt of the Mossberg Model 500 uses a single locking lug that cams upwards into a matching hole in the barrel extension. A sliding safety is positioned on the rear hump of the receiver, and a bolt-release button protrudes slightly from the left rear of the trigger guard. The action is operated by twin action bars that prevent the torsion and binding which plagued some earlier pump shotgun designs.
The FLEX 500 is the newest variant of this 52 year-old design. It uses rugged and simple quick-release fittings to swap out buttstocks, fore-ends and recoil pads. This allows the shooter to use a single receiver as the core component for many different shotguns.
In this video, the Mossberg 500 FLEX transforms without tools from a short-barreled tactical shotgun to a ported, long-barrel waterfowl gun with interchangeable choke tubes in just over one minute. And that minute includes about 20 seconds of me fumbling with the fore-end. I’d done it dozens of times before, but I must have gotten camera-shy; apparently I wasn’t ready for my close-up.
Now that I’ve given y’all a refresher course on the Mossberg 500, let’s dive into what’s new about the FLEX 500: the quick-detachable pieces-parts.
Instead of a long screw that runs inside the buttstock (which is so 1961), FLEX 500 buttstocks attach to a sturdy quick-detach stock lug at the rear of the receiver. To detach the stock, make sure the gun is empty and open. Then just pull up the locking pin behind the tang, rotate it 90 degrees, and pull the stock off of the lug. Attaching a new stock is the same process in reverse: put the stock on the lug, rotate the locking pin, and push it down into place. As the videos show, it takes only seconds.
When I saw the FLEX system at the SHOT Show, I dismissed it as a flimsy gimmick that would wobble itself loose if you even looked at it cross-wise. I could not have been more wrong: all four of our Mossberg’s buttstocks fit very snugly, with absolutely no play or wobble, and I sometimes had to give the joint a couple of thumps with my palm to knock it loose. Even after about 300 rounds they’re still as tight as they were the day I picked them up from my FFL months ago.
Straight buttstocks are offered in short, medium and long sizes, and several different sizes of FLEX recoil pads snap into them. Push two buttons at the toe of the buttstock and the recoil pad falls off; slap a new one into place and you’re back in action.
Mixing and matching buttstocks and recoil pads lets you make this gun comfortable for anyone from a petite 5’0″ teenager to a 6’3″ Marine. I’m 6’0″ myself, and I was most comfortable with the longest stock and the thinnest recoil pad.
A collapsible M4-style pistol grip buttstock is also available. It’s solidly built and adjusts from 11″ to 14.25″ length of pull, but I wasn’t impressed by its shooting ergonomics. M4 buttstocks were designed for the straight-line recoil axis of an AR-15 and their geometry doesn’t adapt well to the dropping buttstocks of conventional shotguns. They do work pretty well on shotguns with elevated front and rear sights, but the 500 isn’t one of those.
The M4 buttstock has one ergonomic advantage: your thumb can’t smash you in the nose if you forget to keep it up on the tang safety as shown here. This advantage, sadly, is perfectly counterbalanced by corresponding disadvantages: 1) I couldn’t reach the safety at all without taking my hand from the pistol grip; and 2) the dropping M4-style extension tube repeatedly smashed me in the cheek, sometimes even with light loads. All in all, I’d have to Just Say No to the M4 buttstock on a shotgun like this.
And while you’re at it, say no to the ‘Cruiser’ pistol grip also. As Massad Ayoob sagely notes, stockless shotguns have all the disadvantages of a long gun (bulk, weight, too easy to grapple) and all the disadvantages of a pistol (unstable firing position, low hit probability, useless in hand-to-hand combat) with almost none of the advantages of either. The FLEX Cruiser-grip is very sturdy and not too painful to shoot (with light loads) but the best thing about it is that it’s very easy to replace it with a properly functional buttstock.
The 500 FLEX can swap fore-ends quicker than Greg Biffle’s NASCAR pit crew can swap tires. Mossberg sells three different fore-end styles. A basic black polymer unit comes with the gun, but you can upgrade to a Realtree Advantage camo pattern for $30 or a railed ‘tactical’ style for $35. Contrary to my initial preference, I strongly recommend the railed fore-end upgrade if your 500 FLEX will see any defensive duty.
I was a huge un-believer in railed fore-ends on pump shotguns, ever since I cheese-gratered my left hand shooting Iain Harrison’s loaner at last year’s Midnight 3-Gun Invitational. Despite this, I really like the FLEX 500 railed fore-end. The polymer rail sections are nicely de-horned so they can’t trash your hand or saw through your gear. Another cool feature is that the sides of the fore-end include recessed Velcro panels for remote pressure switches for lasers or weapon lights. When you’re not using any pressure switches, the Velcro panels have soft rubberized covers that provide a better grip than the plain fore-end.
The FLEX 500 uses any standard Mossberg 500 barrel, so your choices are basically endless. Our tester came with an 18.5″ cylinder-bore barrel with a breaching muzzle and a fiber front bead.This barrel grouped well with 2.75″ Royal 00 Buck, delivering slightly better the expected pellet dispersion of one inch per yard of distance. We didn’t test with a wide range of buckshot, since even low-priced buckshot is $.75 a round, and every gun patterns differently anyway. This barrel was also happy with the mixed bag of slugs we fired through it. Even with its fairly crude fiber-optic front bead, we kept all our shots on our 3/4 scale steel silhouette at 60 yards firing offhand.
Our tester also came with a 28″ ported vent-rib barrel with dual beads and interchangeable Accu-Set choke tubes. I brought a few friends to help shoot the Mossberg, and we dusted an entire box of clay pigeons (singles and doubles) from hand throwers. Being able to adjust the length of pull to each shooter was a huge plus; we all shot to the limit of our ability without having to fight the gun.
Our FLEX kit came with a rather short two-point sling and the front sling stud unscrews so you can swap it from barrel to barrel. The screw-in stud doesn’t have a captive lock-washer or many extra threads. It’s not inconcievable that it could wiggle loose under recoil or unscrew itself if your sling gets all twisted up. It’s a very minor complaint, but sling studs should be captured in the barrel tightening nut so they can serve as true ‘swivels’ and never get lost.
Perhaps my fondness is born of long familiarity, but I’ve always found the slide release and safety controls of the Mossberg to be safer and more user-friendly than those of the rival Remington 870. There’s no way your finger can slip onto the trigger and cause an AD while you’re manipulating a Mossberg safety, and you don’t have to displace your strong hand as far to activate the slide release.
When it comes to the fit of this shotgun to the shooter, almost every dimension of this stock can be configured the way you want it except the drop and cast of the stock. The trigger pull is exceptionally smooth and light for a shotgun, and better than most big-box store bolt-action rifles. Mossberg has been building these twin action-bar receivers since my dad was a teenager, and today’s 500s have a very smooth (if not terribly short) pump action.
The FLEX 500 has lightweight polymer furniture, an alloy receiver and a 5-round magazine tube so it’s no heavyweight platform to begin with. This makes it a breeze to carry, but with a short breaching barrel it will punish you with heavy buckshot or slug loads. Recoil was substantially heavier with the 500 than with the 930 Tactical that I recently tested. When we attached the 28″ ribbed barrel, the added mass (and the porting) made recoil a lot more manageable.
Although the FLEX 500’s stock can be configured to fit smaller shooters, this is not the best gun for a small-framed teenager who’s just learning to shoot. Anything but the lightest target loads kick vigorously with the short barrel.
Mossberg equips some shotguns with their LPA or ‘Lightning Pump Action’ trigger. Resembling a Savage ‘Accu-Trigger’, the LPA features a skeletonized inner trigger which releases the sear and fires the gun, mounted within a wider outer trigger that is adjustable for pull weight. The turn of a single screw will dial in any trigger pull between 3 pounds and 7 pounds and ours came preset for just four pounds. This might seem awfully light for a utility shotgun, but let me tell you it’s really easy to get used to a short, sweet trigger pull with no grit and only a little overtravel. Even shotguns benefit from good triggers, more than you’d expect.
My only issue with the LPA trigger turns out to be a purely hypothetical one: if you somehow manage to pull the outer trigger without pulling the skeletonized inner trigger, there’s a distinct ‘click’ inside the lockwork and the gun will not fire until you manually press the slide release and work the slide. If it happened in a high-stress situation you would have a jammed gun in your hands, so I don’t like it.
However, this never actually happened through all the 300+ rounds we fired. Total noobs and veteran shooters used the FLEX 500 to shoot clay pigeons and 3-gun stages and pumpkins for many hours over several shooting days. We never had a single problem with the trigger, so I’ll put aside this concern unless or until it becomes an actual problem.
Fit And Finish
It doesn’t have the deep bone-charcoal bluing of a prewar Winchester Model 21 (and what does?) but the FLEX 500 is really well put together for a utility-grade shotgun. Although it shares almost 100% parts commonality with my own 1970s-era Mossberg 500, they don’t even feel like the same model of shotgun in your hands. There’s no shake, rattle or roll in the new action, and the metal finishes are a deep phosphated black instead of a thin blue or anodized finish.
The magazine tube is cemented into place, which will make it a chore if you want to slap a Model 590 barrel and magazine tube onto your 500 FLEX receiver. If this be your plan, Mossberg also sells a FLEX 590 and you should just buy it up-front. If you need to reduce the magazine capacity for waterfowl season, it’s really simple: you just slip a short, thin wooden dowel into the little hole at the end of the mag tube and call it good. The gun comes with just such a dowel, which I immediately removed and promptly lost. Canada geese may taste better than bowling pins and steel targets, but it’s not waterfowl season yet.
The cemented mag tube will complicate your life when the time comes to replace the magazine spring. My experience is that the springs last about five years if you leave a shotgun loaded to one short of its magazine capacity. A lot of Mossberg 500s see double duty as hunting and defensive arms (the Flex is particularly suited for this) and I’ve had to replace the magazine springs of every one of the three pump shotguns I’ve owned. This is a very simple DIY repair job, but that blob of cement would make it a real PITA which would probably need a gunsmith’s attention if you don’t want to screw up the metal finish with acetone.
My friends, several of their kids and I shot the ever-lovin’ crap out of this gun. Total round count: over 300 rounds of birdshot, 40 rounds of buckshot and more than a dozen slugs. Total malfunctions: none. I’m happy to keep testing it if you’ll send me more ammo, but I don’t think there’s too much left to prove. This shotgun is battle-proven and battle-ready.
The Mossberg 500 is a familiar and proven platform. So why did Mossberg fix something that certainly isn’t broken? Well, it’s not so much a repair as an improvement: the already-versatile 500 is now even more adaptable and versatile than before. If you’ve got a young and growing shooter in your family, being able to quickly switch out buttstocks and recoil pads for a proper fit is by itself worth the slightly higher price of a 500 FLEX compared to a regular Mossberg 500. And if you’re on a budget and your goose gun spends most of the year as your home defense shotgun, the easily-configured buttstocks and fore-ends make a lot of sense for just a little extra money.
I’ve already got a Mossberg 500 and I’ve already got a dedicated defensive shotgun, but the improved fit and finish of this new 500 is so dramatic that I’m strongly considering purchasing one for myself and passing down the old Mossy to a family member. Yeah, I like it.
Type: Pump-Action Shotgun, twin action bars.
Caliber: 12-guage, fires 2.75″ and 3″ shells.
Barrel: 18.5″ cylinder-bore with breaching muzzle and fiber-optic front bead (tested), 28″ ported vent-rib barrel with dual brass beads and interchangeable Accu-Set choke tubes. Many other barrels available.
Magazine: Tubular underbarrel magazine, 5+1 round capacity.
Trigger: Lightning Pump Action trigger, adjustable from 3.0 to 7.0 pounds. 4 pounds as tested.
Stock: Polymer stock and fore-end, with numerous configurations and lengths of pull available.
Finish: Matte black phosphate finish.
Weight: 7.5 pounds in hunting configuration. Varies depending on hardware and barrel length.
MSRP: $661 (street price $375-550, depending on how many barrels and stock components are included).
Manufacturer’s Website: http://www.mossberg.com/products/shotguns/mossberg-flex/flex-500-all-purpose
RATINGS (Out Of Five Stars)
Reliability (gun): * * * * * (FLEX system): * * * * *
The Mossberg 500 is already legendary, and ours was no disgrace to its ancestors. No misfeeds, duds, ejection hangups or short-strokes in more than 300 rounds fired. The FLEX system proved to be completely dependable as well. Every component locked in place and stayed there, no matter what we did to it.
Ergonomics * * * * 1/2
The 500 has good user controls to begin with, but the FLEX 500 has big improvements over my old 500. It’s got an awesome trigger, and you can instantly configure the stock to your proper length of pull. You’ll really notice a proper fit in your 3-gun or sporting clays scores.
Aesthetics: * * *
Not much to lust after in a solid utility-grade shotgun, but any gun that works this well looks just fine in my book.
Customize This: * * * * *
Mossberg 500s were already among the most customizable guns on the planet, and now they’re even more so. Anything and everything is adjustable or instantly replaceable.
Overall Rating: * * * * *
Quite possibly One (Pump) Shotgun To Rule Them All. Anyone looking for a multipurpose utility-grade shotgun should look here first.