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Review: Smith & Wesson M&P 15-22 SMU Rifle

From the vast pool of various .22-caliber rimfire carbines available today, Smith & Wesson’s M&P 15-22 rimfire series has always stood out because this rimfire series takes after the actual dimensions and manual-of-arms of an AR-15. Since the M&P 15’s 2009 debut, Smith & Wesson has done a good job keeping the M&P 15-22 series relevant with the times and the new M&P 15-22 SMU continues that tradition.

Smith & Wesson M&P 15-22 SMU Overview

This new version includes a modern B5 Systems carbine stock and B5 pistol grip. The rifle is built on a proprietary flat-top upper receiver and incorporates a contemporary M-Lok tubular handguard with a span of Picatinny rail along the top. The M&P 15-22 also comes equipped with a set of polymer Magpul MBUS front and rear folding sights. Internally, a reliable blowback rimfire action cycles .22LR cartridges and launches them through a 16.5-inch barrel. The barrel has industry-standard ½X28-inch threads and an A2-style flash-hider. Except for the action, barrel and a few parts, the M&P 15-22 is wholly built from polymer. The lower receiver, upper receiver and handguard are polymer; all Picatinny rail surfaces and parts like the proprietary charging handle and safety selector are polymer also. Only a few parts aren’t polymer, like the bolt-catch, mag-catch, take-down pins and the actual trigger unit. In this case, it consists of a standard single-stage USGI trigger with its typical break and pull-weight. 

Although the action works nothing like the standard AR-15 direct gas-impingement mechanism, the M&P 15-22 field strips the same, by sliding the rear take-down pin and pulling out the rimfire bolt and charging handle from behind. Its receiver extension is solid and directly molded into the lower receiver itself. There is no end-plate or castle-nut holding it in place. This mock receiver extension accepts any standard AR-15 carbine stock, like the included B5 stock. Perhaps the only visual giveaway that would cue someone to notice that it’s not a true 5.56 NATO carbine would be the ejection port. Not only is its port considerably shorter, but it also lacks the typical hinged dust-cover.

Outfitting The M&P 15-22 

Prior to shooting, I outfitted the M&P 15-22 the same way as other 5.56 NATO carbines with 16-inch barrels that I’d recently been shooting and mounted a Leupold Mk.5 HD 2-10×30 and an offset 45-degree Gideon Omega reflex sight. This specific combination allows for both precision and speed by simply tilting the carbine to the side. I’m conducting a long-term evaluation on this particular optics suite and having the chance to shoot it more with cheaper ammunition. And as a plus, this scope set at 10X power made it extremely easy to shoot for accuracy at 50 yards. Beyond optics, I attached a Magpul MS1 2-point sling. The B5 stock has built-in QD sockets, so I put a QD swivel on the sling’s rear-end. The M&P 15-22’s polymer M-LOK handguard lacks sockets, so I rigged a loop of paracord through one of the slots and looped the sling through the paracord.

M&P 15-22 Accuracy & Reliability 

I spent an afternoon shooting several hundred rounds of assorted .22LR rimfire cartridges (approximately 450 to 500) with the M&P 15-22 both off a bench and standing. The assortment included a mixture of Winchester Super-X 40-grain HP Power-Point, Winchester Subsonic Max 42-grain HP, Remington Golden Bullet HP, CCI Mini-Mag 36-grain HP, Federal Punch 29-grain HP, Federal AutoMatch 40-grain RN, Federal Standard 40-grain RN, CCI Standard 40-grain RN and an assortment of miscellaneous Winchester RN cartridges. 

I included the first four rimfire varieties in the official 50-yard accuracy report as common and less expensive bulk rimfire ammo as it’s likely what most people shoot through guns like the M&P 15-22. I shot the other ammo types at different distances both slowly and quickly with the intention of seeing how the carbine handled them. With the aid of the excellent Leupold Mk.5 HD at 10x, the mean of all group sizes was 1.77  inches. This carbine also showed an affinity for Remington Golden Bullets as it printed slightly tighter groups compared to other rounds. Out of curiosity, I did shoot a 10-round group of Federal’s relatively new Punch defensive rounds through the carbine at 50 yards. Although the group was larger than everything else, about the size of a closed fist, it still fit in an A-zone, meaning it would yield reasonable defensive accuracy at closer distances. I suspect the groups were a result of the 29-grain Punch bullet being too light for the rifling twist found in the M&P 15-22.

The Takeaway

Overall, the Smith & Wesson M&P 15-22 carbine is reliable and had no problem igniting and cycling virtually all ammo types I put through it. Though the ammo list isn’t comprehensive, I get the impression that the M&P 15-22 can handle mostly any standard 36- to 40-grain .22LR cartridge just fine. I went the entire afternoon review session with no more than two cartridges which didn’t ignite and that’s something to be expected with bulk rimfire ammo. In the course of the review, I did find the supplied 25-round magazines to be temperamental. Out of the three I worked with, the followers in one of them kept binding on its own along its track and induced several malfunctions, regardless of ammo type. I set this unit aside and worked with the remaining two magazines I had. I’m still lukewarm about the magazines and I think the springs could use more strength in general. Even with one of the better mags, I had occasional malfunctions where rounds would nosedive from the follower spring buckling under the tension, especially when loading close to or at capacity. For best results, it pays to load each cartridge carefully at a time ensuring that its nose sits at an upward angle and that the follower doesn’t lose contact. Loading 10 or fewer rounds yielded almost no issues, and outside of this review, I’m new to the M&P 15-22 platform. I’m not sure if the supplied magazines simply weren’t up to par or if they require a bit of a break-in for smoother follower travel. My only other complaint is that the polymer safety-selector lever felt very stiff rotating inside the polymer lower. 

Taking a .22LR carbine and designing it to resemble and operate like a standard AR-15 is an idea with wide appeal. Not only is shooting such guns extremely fun, some shooters will find value in having a correctly-sized “trainer” with the same controls that also fires cheaper ammunition. My take is that no substitute can take the place of training with the genuine article, but there is something to be said about having a sub-caliber carbine that works nearly identically. Besides fun, the biggest value I see from the M&P 15-22 is the ability to use it as an optics test-bed, like I did with the aforementioned Leupold Mk. 5 HD 2-10×30 scope and the offset Gideon dot. For AR-15 centric use, I can’t think of a better way to get a feel for optics while spending a lot less every time I pull the trigger.  

50-Yard Accuracy Report: 

Ammo: 22LR

Minimum Group

Average Group

Largest Group

Winchester 42-grain HP Subsonic Max




Winchester 40-grain HP Super-X Power-Point




Federal 40-grain RN AutoMatch




CCI 36-grain HP Mini-Mag




Remington 36-grain HP Golden Bullet





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