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Smith & Wesson M&P 5.7: Best Gas Piston Pistol?

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After languishing in the “almost-made-it” doldrums for years, the 5.7x28mm is experiencing a bit of a resurgence, with a half-dozen or so new guns chambered for the pipsqueak round. Smith & Wesson is the latest to enter the fray, and they’ve taken a completely different approach from everyone else with the gas-operated M&P. 

In today’s world of plastic-framed, striker-fired, 9mm uniformity, the Smith 5.7 is like standing on a mountain top in baggy shorts. It’s a waft of cool, refreshing air across the sweaty gonads of an industry not known for out-of-the-box thinking. While the new pistol may look like the rest of the M&P lineup, it’s completely different under the skin, so let’s dive in and look at what makes it tick.

We might as well get to the heart of the matter right away. The 5.7x28mm round was developed in the closing years of the Cold War, in order to give blanket stackers, drivers, cooks, and bottle washers a way of defending themselves when Soviet motor rifle regiments equipped with AK-74s came knocking on the door. 

It was never intended as an assault rifle cartridge, but rather as the bare minimum needed to give support troops a fighting chance, given their rather mediocre level of small arms proficiency. 

Looks like a standard striker-fire slide, but looks can be deceiving: there’s a hammer hidden inside.

So it was unintimidating and easy to shoot, with minimal recoil and muzzle blast, and the guns wrapped around it could be made smaller and lighter — handy if you’re jumping in and out of vehicles all day or have your hands full with other tasks. 

This lack of recoil meant that sticking the tiny cartridge into a recoil-operated firearm was a non-starter; it just didn’t have the mass needed to reliably work a Browning-style tilting barrel mechanism, so it was fielded in a variety of blowback-operated guns.

The cartridge exists in the margins between operating systems. Unlike say, .22LR, the 5.7 round is a pretty high-pressure little fella, so straight blowback operation requires the use of a heavy slide or bolt in order to retard the breech from opening too soon, a negative if you’re trying to make the gun light and unobtrusive. 

So a variety of retarded blowback designs came to prominence, such as the FN P90, Five-seveN pistol, and most recently Ruger 57, where the barrel recoils a short distance before stopping. S&W took a different course. The company deems this a gas-operated pistol, but in reality, it’s a recoil-operated, rotary-locked, gas-assisted design. 

Smith kept the classic looks while packing a whole lot of new under the hood. The blade safety on the trigger stands out, and of course the large grip to accommodate 22 rounds of 5.7.

There are three critical components to this system. The first is the slide, which is fairly conventional with the exception of locking recesses cut into the left wall, just ahead of the breech face, and a feed horn like that found on some SMGs. 

This latter feature requires the use of a robust extractor with a wide swing, as rather than slip under the extractor hook like in a 1911, the extractor must snap over the cartridge rim as the slide goes into battery. 

There’s been a lot of effort put into lightening the slide, with both internal and external profiling cuts bringing the weight down to below 10 ounces, contributing to its recoil characteristics. While from the outside the slide looks like any other in the M&P lineup, it’s hammer-fired, rather than striker-fired, with an internal hammer block safety. 

There’s no need for a booster or Neilson device when shooting suppressed due to the threaded, fixed shroud.

The rest of the handgun is classic M&P, with a glass-filled polymer frame, ambidextrous slide release, and reversible mag catch. Although the trigger has the usual blade safety in its face, it releases a fully cocked, single action hammer, so trigger pull is surprisingly good. Breaking at 4 pounds, there’s about 3/8 of an inch of take-up before the wall, a crisp break, and minimal overtravel. 

Should you prefer an ambi manual safety, that option is available. And if you don’t, the corresponding frame cutout is blanked off. Mags are stainless, double-column, two-position feed, and 22-round capacity, and you’ll come to appreciate the loading tool that ships in the box.

The barrel is where things get a bit hinky, but in a good way. Secured to the frame via the takedown pin is a sleeve that serves as both gas block and cam path for the barrel that rides inside it. 

The last 5/8 of an inch of barrel are reduced in diameter down to 0.340 inch, and there’s a 1/8-inch area behind this containing the gas port that fits tightly into the sleeve, securing the muzzle end. 

Four gas rings are cut into the barrel behind it, with a further three pseudo gas rings ahead of the chamber that do nothing other than provide a bearing surface and reduce weight. Finally, at the breech end are two locking lugs that engage the slide and a teardrop-shaped cam pin that engages a corresponding path in the barrel sleeve.

Upon firing, the barrel is secured to the slide by means of the two locking lugs engaging their corresponding recesses. As the bullet travels up the bore, Newton’s third law comes into effect and the barrel and slide start to recoil. Because they weigh roughly 150 times more than a 40-grain bullet, they move considerably less and would probably fail to cycle were it not for the final shove given by propellant gases venting into the barrel shroud. 

Standard 1/2×28 threads make for endless muzzle device selection.

This little kick is enough to accelerate the slide rearward to rotate the barrel via the shroud’s cam path and unlock the breech, leading to the familiar process of extraction, ejection, and feeding, while waste gases are vented out the shroud’s muzzle end. 

The unlocking process of a Browning-style tilting barrel is a fairly violent affair, subjecting the takedown pin and lugs to severe stress. By comparison, this rotary locking system should see less force exerted on its components, useful when dealing with a handgun round operating at rifle pressures. There’s a big advantage when it comes to suppressor use, too. Because any can screws onto the immobile barrel shroud, there’s no need for a Neilson device to ensure reliability — and no POI shift, either. 

Reloaders should experience an additional benefit. The current selection of 5.7 ammo is not extensive, so those of us who want spicier loads or different projectiles are forced to roll our own, but a combination of tiny cases and delayed blowback actions presents an additional hurdle. 

During firing, cases stretch more than most bottleneck cartridges and to aid extraction, there’s a special coating applied to the brass by the factory, neither of which is a factor when dealing with a locked breech design.


After bolting up an unobtrusive Bushnell red dot to the Smith’s slide, we headed to the range to zero and get a few first impressions. Not wanting to expend the good stuff on function testing and dialing the dot, ammo for this exercise was humdrum Federal American Eagle FMJ, which is not exactly noted for being a speed demon. 

Despite this, all cases were ejected vigorously, landing in a neat pile about 10 feet away at the 4 o’clock position. While we weren’t expecting flinch-inducing recoil from the tiny round, it was notable for being easy to track the dot, even in the 24mm window of the RSX-250. 

About halfway through the third 22-round magazine, we had a “click, no bang” moment. Immediate action drills failed to do anything other than dump live rounds on the deck, so it was back to the bench to find out what was wrong. Tearing down the pistol, we discovered that the firing pin had sheared at the spot where it reduces in diameter, and the forward part was nowhere to be found. 

When folks started making 9mm 1911’s way back in the land that time forgot, it was quickly discovered they needed a smaller diameter firing pin, otherwise material from the primer cup would creep into the firing pin hole. 

This led to all sorts of interesting events, including wedging the firing pin in the forward position, producing slam-fires, full auto shenanigans, and out-of-battery detonations. It would seem that the pressures produced by the 5.7mm require similar design considerations, as this one’s needle-thin.

On hearing about their new baby sh*tting the bed, Smith’s customer service department was Johnny-on-the spot with sending out a replacement part. Although swapping out firing pins isn’t covered in the user manual, it’s easy enough to do if you’re familiar with tearing down other handguns. Hopefully, this won’t be a common fault with the pistol, but we’ve heard from our freelancers of other teething problems, including magazine issues and failure to cycle certain ammo. So far this has been the only issue we’ve found with this particular pistol.

Once back up and running, we had no trouble holding 4-inch groups at 50 yards and experienced no further stoppages. If you plan on adding a suppressor to the Smith, don’t plan on recovering your brass, as the ejection pattern changes from emphatic to HK G3, launch-the-empties-into-the-next-bay, a by-product of the gas-assisted design.

Overall, we were impressed by the level of innovation embodied in the newest 5.7 pistol to hit the market — dodgy firing pin notwithstanding. Whether this was a one-off problem caused by an inclusion in the steel or symptomatic of a wider engineering issue, we’re not qualified to say, but it doesn’t detract from the thought that went into the package as a whole. 

If it proves to be an aberration, then the Smith ought to be crowned as the best 5.7 handgun out there. If not …

Smith & Wesson M&P 5.7

  • Caliber: 5.7×28
  • Capacity: 22 rounds
  • Barrel length: 5 inches
  • Overall Length: 8.5 inches
  • Weight: 27 ounces
  • MSRP: $700

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