Review: SIG Sauer MPX Pistol

posted on February 14, 2018

This review ran initially in the November 2015 issue of Shooting Illustrated. SIG Sauer has since upgraded the MPX lineup with shortened barrel lengths, new handguard designs and other models, including short-barreled rifles and carbines.

Something goes bump in the night. What’s the ideal firearm to pick up, a rifle, a shotgun or a handgun? Most often, the debate comes down to shotgun or carbine, with valid points made for either platform depending on individual circumstances. Very rarely are pistols thought of as a first line of defense, generally owing to lesser muzzle energy from pistol cartridges and greater practice needed for proficiency. However, a look at the SIG Sauer MPX pistol might change a few minds.

One common knock against rifles or shotguns centers on the overall bulky size of either. Navigating a narrow hallway with a 20-inch-barreled shotgun, there’s plenty of opportunity for Mr. Murphy to help get that long barrel caught on a door frame or other protrusion. Even the ultra-handy AR-15-style carbine requires a little extra room to maneuver—if there are tight confines in your domicile, anything with a lengthy barrel can be difficult to employ.

In cases like these, a pistol like the SIG Sauer MPX might fit your needs. Since it’s a home-defense arm, though, many of the concessions we endure in a concealed-carry handgun don’t apply. Weight doesn’t have to be kept to a minimum, meaning that recoil will be greatly reduced. Accessories can be added without worrying about finding a holster to fit. The shorter barrel and overall length mean sound suppressors can be added without making the firearm excessively long. 

It’s all about trade-offs—while a pump-action 12-gauge offers serious stopping power, it’s heavy, bulky and has a low-capacity. An M4-style carbine is lighter and has greater capacity, while still maintaining decent stopping power, but in the tight confines of a home can be painfully loud. Adding a suppressor negates the advantage of a shorter barrel. While a handgun offers less stopping power than a rifle or shotgun, individual circumstances might make certain models a good fit for home defense.

Clockwise from Left: The company opted for an AR-15-style charging handle rather than a side-mounted variant on the SIG Sauer MPX. Protected by stout ears and folding flat against the rail, the metal front sight is adjustable for elevation. Containing two separate apertures for varying distances, the rear sight also folds flat should optics be desired.

The SIG Sauer MPX pistol is just such a fit. With a Picatinny rail spanning the entire top of the pistol, adding a red-dot or holographic sight for faster target acquisition is simple and still leaves room for iron sights. The rail-ready fore-end can have a weaponlight attached along with a laser, allowing for rapid identification and immediate on-target capability. A convenient QD sling mount allows the MPX to be carried on a single-point sling, leaving your hands free if needed. Should sound suppression be desired, SIG offers a number of options—including a short suppressor that reduces the sound signature while adding minimal extra length.

When the company developed the SIG Sauer MPX pistol, it was designed to be a pistol-caliber (hence the “P” in “MPX”), short-barreled rifle (SBR) and submachine gun. Obviously, the MPX was brought to the drawing board with law-enforcement and military applications in mind. With the civilian market locked out of new fully automatic firearms, the MPX was squarely aimed at the government market served by submachine guns like the iconic Heckler & Koch (H&K) MP5.

It was a bold move to offer a new, pistol-caliber submachine gun in the wake of the growing popularity of mid-range, rifle-caliber arms. John Brasseur, director of product/project management for SIG Sauer, explained, “We’ve seen police/military back away from pistol calibers recently, with either short-barrel rifle calibers (think LWRC PDW) or newer rounds like the 4.6 mm (H&K MP7) or 5.7 mm (FN PS90). Heck, even H&K’s UMP didn’t do all that well. Why a new subgun in pistol calibers?  Better question is why not do what everyone loves and wants, there are a bunch of companies taking ARs and converting them to 9 mm, which is not optimal for that round.”

(l.) A birdcage-style flash hider on the SIG Sauer MPX can be removed in favor of a sound suppressor, as the barrel is threaded for such safety devices. (r.) Two-inch sections of rail can be screwed directly into the fore-end in myriad positions to attach accessories.

Brasseur continued, “We decided to build from the ground up a new platform based on AR controls that people are familiar with, a product that is competitive with the well-known MP5. The MP5 is a very desirable and respected gun in military, LE and, for those lucky enough to get one, commercial circles. Our goal was to build a gun that would be the next generation of MP5s for the world.”

Wanting to include the sizeable U.S. civilian market in the prospective client pool, a semi-automatic pistol version joined the SIG Sauer MPX family. While the SBR version is available to most civilians—provided they jump through the appropriate hoops and pay the NFA tax—the submachine gun version is unavailable. Wanting a civilian-legal version as close to the original design as possible, SIG decided to offer a pistol-only version, and hence the MPX-P was born.

Utilizing a closed and locked, short-stroke pushrod gas system, the SIG Sauer MPX pistol functions in much the same manner as a piston-driven AR-15. The rotating bolt is obviously the biggest difference, and represented the biggest challenge for SIG in bringing the MPX online. Brasseur explained, “Our biggest engineering obstacle was dealing with the gas system and rotating-bolt design. This was a major engineering task that took a lot of hard work and analytical evaluation to overcome.”

(l.) Ambidextrous controls make the SIG Sauer MPX easy to use for both righties and lefties. (r.) Obviously patterned after the standard AR-15, the ejection port on the MPX has a fitted dust cover.

Similarity to the AR-15 is quite evident in the SIG Sauer MPX pistol’s operation, which is unquestionably aimed at those familiar with America’s rifle. The pistol separates into an upper and lower receiver. All controls are located in the same position as on a standard M4-style carbine. It field-strips almost exactly like a standard AR-15, with the exception of the bolt-carrier group. Since it has no buffer tube, recoil is handled by twin captured springs located above the bolt group.

Controls aren’t just patterned after the AR-15, though. Buttons are enlarged, made more ergonomic and are completely ambidextrous. The magazine release, while in the same geographic location as an AR’s, fills a carved semi-circle, which is precisely where the trigger finger comes to rest when off target—perfect for a reload. The safety selector is identical to that found on America’s rifle, right down to the 90-degree rotation from “safe” to “fire,” which are depicted in the standard pictogram format on both sides of the receiver. 

The ambidextrous safety did result in one detriment during firing, though. With a high-handed grip, the safety selector in the “fire” position tended to dig into the base of my trigger finger. After 100 rounds or so, my finger had a nice little divot. This can be remedied, though, by ex-changing the ambidextrous safety for a single-side model. Alternately, plenty of options exist thinner than the variant found on the test sample. Interchangeability with the AR-15 opens up a large world of after-market parts.

As if the exotic styling wasn’t enough of a giveaway, the distinctive MPX logo on the upper receiver calls attention to the SIG Sauer MPX.

One of the first questions, in my mind, that arises when discussing handguns like the SIG Sauer MPX pistol is quite simple: What does it do that a regular pistol doesn’t? It’s heavier and more expensive than a traditional pistol, yet is chambered in the very familiar 9 mm. In order to have an appeal beyond “because it’s cool” (which, for the record, is a perfectly reasonable response to the question of “Why?”), the MPX needs to offer something more than a standard handgun.

Magazine capacity is one area where the SIG Sauer MPX has an edge. Sure, there are a small handful of factory pistol magazines with capacities of 30 rounds or greater, but the majority of standard full-size handguns carry between 15 and 20 rounds. SIG’s own P226 comes with a 15-round magazine, and protruding 20-round versions are available. The curved, polymer, 30-round Lancer magazine shipped with the MPX has been specifically engineered for superior feeding. Another advantage the MPX enjoys is the longer barrel—8 inches compared with 4.25 to 5 inches in a “regular” handgun. This translates into higher velocities and attendant muzzle energy, along with greater accuracy potential. Additionally, the Picatinny top rail allows instant mounting of a red-dot, reflex or even magnified optic if so desired, further increasing precision and the ease of getting on target.

Takedown is accomplished in a manner quite familiar to fans of the AR-15, and all parts are easy to remove for cleaning and lubrication.

In a home-defense role, the SIG Sauer MPX pistol outfitted with a single-point sling is a formidable option. Smaller than even the shortest SBR, the MPX can be slung quickly, without hindering movement. Bringing the MPX into a “low-ready” position from a rest is measured in fractions of a second, and the overall size makes navigating narrow hallways simple. There’s virtually no barrel beyond the handguard, negating a common concern with rifles should your firearm round the corner before you. Lastly, with 30 rounds of 9 mm +P at the ready, combined with a stable platform equipped with a powerful weaponlight and laser-aiming system, it erases many of the advantages enjoyed by carbines. 

On the range, the MPX performed like, well, a SIG Sauer. In excess of 750 rounds were fired through the MPX, testing a wide variety of ammunition types and bullet weights from ultralight Polycase Inceptor 74-grain ARX bullets to heavy 147-grain SIG JHP projectiles. All ammunition fired and ejected perfectly, with one lone failure to feed experienced throughout. All rounds fired and extracted without a single hitch. Magazines consisting of randomly mixed JHP and FMJ ammo, with bullet weights varying by more than 30 grains, were run, rapid-fire, with no stoppages. If your question is “Can I depend on the MPX in a tight spot?” the answer is an enthusiastic yes.

Something that often gets overlooked when discussing firearms is the “fun factor.” Fans of campy ’80s movies will enjoy a stand-in for the ubiquitous but questionable TEC-9 that graced so many of the period’s action films. The SIG Sauer MPX pistol, though, can fire more than FMJs—and in excess of a dozen rounds or so in a row—without jamming. Not every firearm purchase has to be utilitarian; having a gun because it looks cool can be all the reason we need. With the MPX, it looks cool and it works well. 

While few would debate the effectiveness of a pistol caliber over a rifle caliber in pure stopping power, we live in a world of trade-offs. Overall length of one’s defensive firearm, how recoil affects second-shot capabilities, even the ability to keep one type of firearm in a vehicle all play into our choices for a defensive tool. If you’ve decided that pistol-caliber is the way you want to go—or you just want something different—the SIG Sauer MPX pistol is a worthy option.


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