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A Pump for Every Purpose: Mossberg Flex Review

by G&A Staff   |  March 22nd, 2012 23

Mossberg Flex

Last fall, Mossberg’s Vice President of Marketing, Tom Taylor, invited me down to South Carolina for a couple days to show me something he called “revolutionary.” I asked him for a hint, and he replied, “All I can tell you is it involves the Model 500.”

What, I thought, could possibly be revolutionary about the M500 shotgun? It just about defines the workhorse, white-bread, no-frills pump. I was silent for a moment, and Tom, sensing my hesitation, said, “Trust me. It’ll be worth your time.”

“OK.” I replied.

“You won’t regret it,” he said.

And I didn’t. What he had to show me was the new Flex system for the M500 (and M590 3-inch). The Flex permits you to instantly customize, configure and accessorize a shotgun with a wide variety of stocks, fore-ends, recoil pads and barrels using Mossberg’s unique Tool-less Locking  system. The TLS consists of a series of three connectors that allow a simple, tool-free method of switching stocks, fore-ends and recoil pads for any conceivable shotgun application. From a rugged tactical platform to a foul-weather hunting tool to a compact home defense gun, just one receiver does it all.

Flex system stock options include a tactical pistol grip and three all-purpose synthetic stocks in black or a choice of two camo patterns, each with a different fixed length of pull. Plus, there’s a six-position tactical stock and even a hunting/sporting stock with an adjustable comb. They all lock securely to any Flex system M500 (or M590) receiver via a rigid, metal-to-metal, quick-detachable TLS interface. And you can further adjust the length of pull by choosing one of three different snap-on/snap-off Flex system recoil pads in three different thicknesses. This allows for even more custom fit depending on the shooting applications, the amount of outerwear and the shooter’s stature. These attach to the stock via the second of the three new TLS latching systems. Flex system synthetic fore-ends range from tactical railed design to standard field and hunting shapes in black and various camo patterns so you can configure your gun to any purpose—on the fly, without tools—using the third TLS mounting mechanism.

The receiver itself is, of course, the proven M500 design, featuring nonbinding twin-action bars, positive steel-to-steel lockup and anti-jam elevator, anodized aluminum body and ambidextrous top-mounted safety. Moreover, any of Mossberg’s existing selection of M500 or M590 12-gauge barrels will fit any Flex system receiver and fore-end—short tactical barrels, vent-rib skeet barrels, camouflaged waterfowl barrels, tight-choked turkey barrels, cantilever-mount full-rifled slug barrels, whatever. The combinations are virtually limitless.

The TLS locking devices are engineered to withstand the hardest use, from combat to hunting.

Mossberg is starting out the Flex system with 11 new M500 and M590 Flex-receiver shotgun configurations ready to go. It has already got a total of 16 different aftermarket Flex stocks, fore-ends and recoil pads available for further Flexing any of the basic gun setups—plus all the M500 and M590 barrels available. Base model Flex shotguns currently include three M500 All-Purpose, four M500/M590 Tactical and four M500 Hunting options. Three of the M500 Flex All-Purpose and M500 Flex Hunting shotguns feature Mossberg’s Lightning Pump Action adjustable trigger system, which is user-adjustable from three to eight pounds with an Allen wrench to provide a creep-free pull. It’s the best damned factory-issue pump-action shotgun trigger on the market (says this 40-year veteran Illinois slug-gun deer hunter).

M500 Flex All-Purpose Models come with 26- or 28-inch vent rib, Accu-Choke-ported barrels with matte metal finishes or optional all-weather Marinecote finish, plus a full-length matte-black synthetic stock with medium recoil pad for a 141/2-inch LOP and a black matte standard synthetic fore-end. M500/M590 Flex tactical models are available with matte OD green and coyote tan finishes on barrels and receivers, and tactical tri-rail fore-ends that can accommodate a touchpad. Tactical stock options include either standard synthetic, six-position adjustable tactical stock or pistol grip. Barrel choices are either 181/2-inch Stand-Off barrel or 20-inch, both cylinder bore with six-round total capacity (nine rounds with the M590 Tactical). M500 Flex hunting models are available with 24-inch or 28-inch vent-rib barrels and choice of OD green, Coyote Tan, Mossy Oak Break-Up Infinity or Realtree Max-4 camo receiver finishes. Standard full-length stocks and fore-ends feature Infinity or Max-4 finishes as well.

Recommended retail prices currently begin at $593 for a black All Purpose M500 Flex with 28-inch vent-rib barrel and Accu-Choke and go up to $887 for an OD green tactical M500 Flex with 20-inch barrel, railed fore-end and XS ghost-ring sights.

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No Flex in the Flex
When I arrived at the seminar and sat down to listen to the opening presentation, I confess that I was initially less than overwhelmed. There are lots of different stocks, fore-ends, recoil pads and barrels already out there in the marketplace for all major makes and models of shotguns. As for “quick change,” well, I’ve seen many such products that might have fit nicely at the outset, but they quickly became loose after a few on/offs. But as I began to pay closer attention to the details of the three-part Flex TLS mechanisms, I realized there was something different going on here.

The interchangeable recoil pads on the Flex buttstocks attach using two locking studs, which protrude from the pads and are clamped in place by a latching mechanism within the stock itself. The two-sided release panel in the stock is located at its toe and needs to be pressed upward from both sides at the same time to release the internal clamps from the recoil pad studs. The panel is sunken below the stock surface with a shield bar across its middle so that it’s virtually impossible for it to be inadvertently pressed and held down. But when you press it in and hold it, take a firm grasp and pull the recoil pad up and out, it pops right off. And it’s secure as hell. First thing I did when we took the guns out to the range for tryout was pound the butt end sideways as hard as I could against the concrete floor of the firing line before Tom Taylor’s horrified eyes in an effort to knock off the recoil pad. I didn’t succeed.

The fore-ends on the Flex system snap, unlock and lift off (and back on) angularly, with a firm press on a well-shielded pressure point—very much the same motion used to remove the forearm from an old-fashioned double. We worked the Flex fore-ends hard on the ranges, slamming them forward and back, and there wasn’t a hint of loosening.

Of course, the critical element in the Flex system is the interface between the receiver and the stock. That’s where the gun’s recoil energy really comes into focus, and that’s where any shotgun buttstock design is most likely to fail, even stocks meant to be permanently attached. Listening to Mossberg’s Vice President of Engineering, Bill Lutton, explain how the Flex system TLS stock connection worked I was, again, initially dubious.

No way, I thought, that the short aluminum stud coming out of the rear of the Flex receiver was ever going to hold up against 12-gauge recoil without loosening.

No way, I thought, that a release latch as easy to operate with just the thumb and forefinger as he was demonstrating could provide a truly solid lock.

Wrong again, Metcalf.

As Bill continued to explain the tight tolerances in the interface between stock and receiver and the way the slight angles in the lugs holding the receiver stud and the aluminum stud receptacle in the stock in alignment actually serve to tighten their connection rather than let it loosen, I began to appreciate the design. When I got my hands on the system to try it myself, I saw that he was right.

The fit is solid and tight. It’s easy to lift the release latch out of its slot and rotate it 90 degrees to release the lock, but when you go to pull the stock free from the receiver, you need to pull it back straight. The fit is so close that the slightest torque in the direction of pull will bind the closely fitted mating surfaces even more tightly and nothing will move. But it only takes a couple of tries to get the feel of it.

Will it stand up to years and years of countless switching back and forth of different Flex setups? Only tens of thousands of rounds will tell. But during two days of firing as a group, we probably did more on-and-offing between stock types and gun configurations and more pounding on clay targets and slamming down steel targets with different stocks switched back and forth than most individual users will do in a year or more. At the end, everything was still rock solid.

Considering its versatility and ease of custom accessorizing, you should probably think of the Flex as the AR-15 of shotguns.

See photos and specifications of the guns mentioned in this article and order from an inventory of thousands—all online through Gun Locator. Visit


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