Flexing its Muscle: Mossberg MVP Flex Review

Mossberg introduced the initial version of its MVP rifle back in 2011. The name, in case you don't already know, was an acronym for Mossberg Varmint Predator. The rifle had a 24-inch, medium-heavy barrel in 5.56mm NATO, and like variants that would follow, it was built around the popular 4x4 turnbolt action.

Most unusual was the "drop-push" modification to the bolt that enabled it to use AR-15 magazines. A lower section of the bolt face (let's call it a lever) hinges downward behind the feed lips of the magazine to make contact with the head of a cartridge. As the bolt is pushed forward, the lever coaxes the cartridge along until it pops from the magazine just prior to entering the chamber. At that point the face of the bolt pushes it on home.

As a historical note, a similar idea originated at Winchester back in the early 1930s. It was introduced on the Model 54 rifle in .22 Hornet and later carried over to the Model 70 of the same caliber.

About a year after introducing the MVP rifle, Mossberg came up with the Flex system of interchangeable stocks, grips, recoil pads and fore-ends for some of its shotguns. With a quick switch of components, you could transform a hunting gun into a tactical gun or vice versa. Or you could go from black to camo in a flash. And the unique TLS locking system allowed everything to be done without the use of a single tool.

Flex became quite successful for the company, and hunters and shooters kept asking when it would also be available on a rifle.

The answer came in 2013 with the availability of Flex on a new tactical version of the MVP. Only 5.56mm was available through most of the year, but a few rifles in .308 Win. began to trickle out from the factory in late November. Rifling twist rates are 1:9 for the 5.56 and 1:12 for the .308. The .300 BLK is also available, and its barrel has a twist rate of 1:16.

For those who are unfamiliar with the Flex buttstock, an aluminum socket at its front slides over an axle protruding from the rear of the stock proper. Six longitudinal splines on the surface of the axle fit closely into corresponding slots of the socket, preventing rotation of the buttstock under recoil.

Using the fingers to rotate the horizontal pin of the axle 90 degrees locks the buttstock in place. Once that's done, the telescoping handle of the pin is pushed downward for a flush fit with the top of the stock. It works perfectly, and because recoil during firing pulls the two stock sections together, little if any stress is applied to the locking pin.

Mossberg classifies the MVP Flex as a tactical rifle, so the standard version comes with a six-position, AR-style stock. Minimum/maximum adjustments for length of pull range from 11 inches to 14.25 inches. The Youth version wears a stock of more conventional styling and has a pull length of 12.5 inches, and that same style of stock is available as an accessory with pull length options of 13.5 and 14.25 inches. Also available is a hunting-style stock described by Mossberg as four-position that uses the Dual Comb interchangeable comb system. Finish options for it and the standard stock are black and a couple of camo patterns.

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Accessory recoil pads of 0.75-, 1.25- and 1.5-inch thicknesses are also available. Having those, along with the three stocks of different pull lengths, would allow one rifle to be tailored to fit Mom, Dad, all the kids and most of the neighbors as well.

The standard four-position and Youth stocks have 1.25-inch recoil pads, so the other two pads allow length of pull to be shortened or lengthened. If the stock on Junior's Youth rifle happens to be too long, simply switch it for the 0.75-incher. Then, as his arms grow longer, so can the stock. The recoil pad is removed by pushing on a spring-loaded tab at the toe of the stock.

If you prefer to buy a rifle already wearing a 3-9x42 scope, the Scoped Combo is for you.

There are two barrel options, both fluted. One is 20 inches long, of standard weight and comes with or without a flash suppressor and thread protector. (The Youth rifle is not available with a suppressor, but if that's what Junior wants, you could buy the rifle that has one and switch out its stock for the Youth version.)

Mossberg describes the second barrel option as medium bull. It is 18.5 inches long and measures 0.75 inch at the muzzle. Rifles wearing this barrel are also available with or without a flash suppressor and as a Scoped Combo version. All .22 caliber barrels have chambers reamed to 5.56mm NATO dimensions, which means 5.56 and .223 ammo can be used.

Patents do not last forever, and that applies as much to firearms as anything else. For about as long as they have been built, certain design details have been borrowed back and forth among the various firearms companies, and there is no better example than the barrel lock nut on the MVP rifle. The concept was introduced by Savage on its Model 325 rifle back in the 1940s and is still with us today on other rifles from that company. Something that lasts that long has to be good.

The traditional way to fit a barrel to its receiver is to initially chamber it short and then final-ream by hand to the correct headspace. It is a time-consuming operation. By using the lock nut, the barrel can be chambered full-depth by automated machinery and then screwed into the receiver and head-spaced off the bolt. Tightening the nut holds the barrel in place.

Savage originally introduced this method to cut production costs — and it still does — but when both methods are compared on a mass-production basis, it can be more precise as well. The guys at Mossberg were wise in employing this system of barrel attachment.

Mossberg offers five-, 10- and 30-round magazines in the 5.56mm version. A friend of mine has an MVP in 5.56mm and an AR-15. Some of his magazines are from Mossberg, but he also uses others of various brands. He says all interchange between the two rifles quite nicely.

The .308 version was introduced with a 10-round magazine, and while that will remain standard, a five-round magazine will have become available by the time you read this. A 20-rounder is due out during the first quarter of 2014, and a 30-rounder is slated for arrival during mid-summer.

The magazine release is located just forward of the magazine well, and while easy to operate with either hand, it is recessed enough to discourage accidental bumps in the field.

The .308 caliber gun can also be used with M14/M1A magazines. I am told it will accept AR-10 style magazines available from DPMS, but will not work with proprietary ArmaLite AR-10 mags. I did not have any AR-10 magazines on hand, but I do have a Super Match version of Springfield Armory's M1A, and its 10-, 20- and 30-rounders worked in the MVP without a hitch.

Pushing the top two rounds from a 30-round magazine takes a good bit of muscle behind the bolt handle, but all rounds fed just fine. Weighing over 2.5 pounds, a full-up 30-rounder increases the weight of the rifle enough to notice.

A Picatinny rail attached to the MVP Flex's receiver at the factory makes scope mounting easy. The two-position safety lever at the right-hand side of its receiver tang does not lock the bolt from rotation, allowing the chamber to be loaded and unloaded with the safety engaged. A bolt release tab sits on the opposite side of the tang.

The body of the bolt is precision-machined and then spiral-fluted while its handle and cocking piece shroud are steel castings. In the event of a blown primer or ruptured case, propellant gas flowing back between the bolt and the left-hand wall of the receiver would be deflected away from the shooter by an extension of the shroud. Another deflector at the root of the bolt handle further closes off the rear of the receiver. There is also a gas vent located in the left-hand side of the receiver ring, adjacent to the face of the bolt.

The bolt has a floating head with dual-opposed locking lugs and is held in place with a transverse pin. A deeply counter-bored bolt face encloses the head of a chambered cartridge, although its wall is interrupted for passage of a Sako-style extractor. Spent cases are ejected by the familiar spring-loaded plunger. Head diameter of the .308 case is considerably larger than the .223 case, so more of it extends above the feed lips of a magazine. The drop-push lever found on the MVP rifle in .223 is not needed for the .308, although it does require the addition of a couple of small fixed protrusions at the bottom of the bolt head.

The 18.5-inch barrel version I shot arrived with a 30mm Swarovski 1.7-10x42 scope held in place by Warne rings. Total weight, including a fully loaded magazine, was 9.25 pounds. I rounded up three different factory loads and fired five three-shot groups with each at 100 yards, allowing the barrel to cool down for five minutes between each group.

Federal's Gold Medal target load with the Sierra 168-grain MatchKing bullet proved to be the most accurate with Hornady's Superformance loading of the 165-grain GMX a not too distant second. The smallest individual group measured 0.91 inch and was fired with the Hornady 165-grain GMX.

As is to be expected, the rifle has Mossberg's LBA (Lightning Bolt Action) trigger, which is user-adjustable from two to seven pounds. The gun came from the factory adjusted to 34 ounces with a pull-to-pull variation of only two ounces. There was noticeable hesitation about midway through its travel, but by the time I had squeezed off 20 rounds or so, I had become accustomed to it. All cartridges fed from the magazine as smooth as silk, with no malfunctions.

I found that taking off and reattaching the stock caused the first shot to land about six inches off zero, but subsequent shots were always back where they were supposed to be. There was a slight change in zero when going from the standard to the tactical stock, but it was not enough to matter on a deer out to a couple hundred yards.

Short-barreled tactical rifles are popular in law-enforcement circles because they're easy to maneuver in tight places, and the 18.5-inch barrel of the MVP serves that role nicely. But from a hunter's point of view, the standard-weight, 20-inch barrel is the way to go. In addition to reducing weight by about 0.75 pound, it puts muzzle blast a bit farther from the ears and increases velocity by 75 fps or so. Regardless of which barrel you choose, you'll find the MVP Flex quite reliable, accurate enough and loads of fun to shoot.