SIG Sibling Showdown: The MCX Rattler versus MPX Death Match — Full Review

I have two younger brothers. While we are best of friends today, such was not always the case. In our earlier days, we strived vigorously to kill each other.

Brotherhood is an odd thing, and testosterone is the most potent poison known to man. The liberal application of this inimitable toxin within a familial environment can indeed result in some of the most deplorable mischiefs, but it can also be quite beautiful. Though brothers are inevitably competitive, obnoxious, loud, and violent, our bond is both unbreakable and complimentary. We might beat each other senseless with monotonous regularity, but perceive some collective threat from the outside and it’s on.

As I appreciate my two boys juxtaposed against my own fraternal experience I come to grasp that our many manifest differences make us a better whole. One might be stronger, while the other is a bit better at math. Independently we can excel in our own particular pursuits, yet together we can ably move a piano. Brothers bear uncanny similarities and profound differences. It is in such stuff as this we find our true strengths.

The SIG MPX 9mm is a large-frame handgun in the eyes of the BATF. The addi-tion of a Pistol Stabilizing Brace makes it the ultimate home defense weapon.

The Mission

I live half an hour outside of town on my modest rural farm. I count the local Sheriff and his deputies among my dearest friends, but even in a perfect world it will still take them at least a quarter hour to get to my place from a standing start.

I know of three of my immediate neighbors who have been the victims of home invasions in the past five years, two of which occurred while the homes were occupied. In one case the oldest family member present at the time was twelve. Defending yourself against an armed threat in your home is no baseless exercise.

Fortunately, there is an entire robust industry that has arisen around the guns, tactics, and gear required to keep you and your family safe come what may.

Whether the scenario is within your abode, in the local supermarket parking lot when you’ve zipped out late for a gallon of milk, or fleeing the coming zombie apocalypse, the flower of modern American engineering prowess offers you the tools you need to prevail. Amongst a cluttered sea of arms producers marketing their wares to the responsible armed American, nobody does it quite like SIG SAUER.

The SIG Success Story

In 2000 a pair of well-funded European investors purchased a group of five European and American defense companies that included SIGARMS, the immediate predecessor to today’s SIG SAUER. It’s breathtaking to contemplate, but this relatively modest subsidiary of the European SIG Empire sold for a paltry $1 at the time. Now some eighteen years later SIG is the apex predator among US tactical firearms manufacturers.

Not only does SIG produce roughly one million guns a year for consumption by Law Enforcement, military, and civilian end users, they also hold the contract to provide the US military with its new service handgun. With the award of the Modular Handgun System contract, SIG becomes only the third company in history to win a competitive contract for an American service pistol. It turns out that $1 outlay back nearly two decades ago was a remarkably prescient investment.

The SIG MPX sports a KeyMod handguard available in a variety of lengths.

Nowadays SIG’s product offerings literally span the spectrum. From service pistols to concealed carry guns to 1911 variants in a bewildering array of configurations and hues, SIG’s handgun lineup includes something for literally everyone. Their long gun selection runs the gamut from 9mm to 7.62×51 with everything in between. Their product line includes optics, sound suppressors, air guns, ammunition, and gift items. Along the way, the good folks at SIG developed the most efficient home defense weapons available on the American civilian market.

Pursuing Perfection

What is the perfect home defense gun? That simple seven-word query has spilt a river of ink. Arguments have been made for the slide action 12-bore, various handguns, and Modern Sporting Rifles of countless stripes. However, all that pales when compared to the submachine gun.

SMG’s are pistol-caliber carbines designed to be fast handling and maneuverable. They were in their ascendancy during the global hemoclysm that was World War 2 and have steadily been replaced in LE and military service by stubby rifle-caliber weapons in more recent times. For civilian home defense use, however, literally nothing is better.

These little guns are safer and more easily mastered than a handgun, and their prodigious magazine capacity provides an insurance policy if the threat array arrives in herds. These guns typically accept modern electro-optical sighting solutions and will avail themselves of sound suppressors as well. Properly accessorized and wielded by a determined homeowner, such a smoke pole is indeed the top of the tactical heap.

Full auto fire is grossly overrated. Don’t get me wrong; I like producing a recreational brass rainbow just as much as the next guy. That thirty-round grin reliably creases my wizened visage despite a lifetime round count adequate to make the CEO of an ammo plant feel both warm and fuzzy. However, I’d much sooner be chased by some yahoo with a full auto MAC10 than by the same malevolent goober sporting a bolt-action hunting rifle with the will and skill to use it. The fact that our civilian defensive weapons lack a happy switch doesn’t make a lick of difference out here in the Real World.

The barrel of the SIG MPX is free-floated within the handguard. The gas system is piston-driven and requires no adjustment.

SIG makes their own extensive line of premium defensive ammunition in their new Arkansas plant.

Pertinent Particulars

Among SIG’s extensive product offerings, two guns stand out as particularly efficient home defense tools. Both weapons transfer as handguns yet sport collapsible Pistol Stabilizing Braces. Just in case you’ve been living underneath a rock lately, the PSB is an inspired contrivance devised by a Navy veteran named Alex Bosco to allow disabled veterans home from our recent kinetic festivities overseas to run a proper gun safely one-handed.

The BATF, showing remarkably sound judgment, ruled that the addition of one of these delightful devices did not change the host gun’s pistol classification. This ruling opened up a whole new classification in American firearms. As a result, short-barreled pistols sporting a PSB bring most of the efficiency of a subgun without all of the legal hassle.

SIG offers an extensive line of quality sound suppressors. This robust .30-caliber can is built like a tank and provides world-class performance.

Our Contestants—9mm

The hottest of the lot within the SIG lineup are the MPX and the MCX Rattler. The MPX is a closed-bolt, pistol-caliber large-frame handgun that is convertible between 9mm, .357 SIG, and .40 S&W. The MPX uses proprietary 30-round translucent polymer magazines and sports the same controls and manual of arms as your favorite AR rifle.

The charging handle and last round bolt hold open are right where Gene Stoner put them in the first place. The magazine release, bolt catch, and safety are bilateral for easy access. Unusual for a pistol-caliber firearm, the MPX is actually a gas-operated piston-driven design and enjoys an unnaturally smooth firing cycle as a result. Barrels and buttstocks are easily exchanged in the field by the user. Barrel lengths range from a stubby 4.5 inches on up. The gun includes plenty of KeyMod space for accessories, and the barrel is threaded for a muzzle attachment.

The muzzle threads of the MPX are 13.5×1 metric left-handed threads. This precludes the addition of standard flash suppressors and muzzle attachments for good reason. As 9mm and 5.56mm muzzles are both typically both threaded 1/2×28 in America, the use of this thread pitch would allow the addition of a .22-caliber muzzle attachment to the muzzle of a 9mm MPX. Such an appendage would instantly convert your expensive home defense gun into a bomb. However, I landed an inexpensive adaptor online that sits between the MPX muzzle and my SilencerCo Omega 45K sound suppressor. Just don’t inadvertently thread on something with a .22-caliber hole in the end, and you’re good.

The SilencerCo Omega 45K is a sealed stellite and stainless steel can that is compact, efficient, and essentially indestructible. Interchangeable pistons allow for different applications. I use this .45-caliber can on 9mm firearms to great effect simply by exchanging the mounting pistons. The Omega is a superb sound suppressor that represents the current state of the art.

The SIG MCX Rattler is arguably the tiniest production rifle-caliber firearm on the market. Sporting a Pistol Stabilizing Brace and SIG optical sight, the MCX Rattler is disproportionately effective given its compact dimensions.

Now For Something Spunkier

The MCX Rattler is one of the shortest production rifle-caliber AR pistols ever made. The Rattler also sports a collapsible PSB. Based upon an otherwise-stock AR lower receiver, this component of the revolutionary Rattler is the only thing that is standard. The adjustable short-stroke piston-driven gas system is uber-reliable and easily manipulated with either a cartridge tip or a standard finger. The gun’s modular design allows it to be configured with various barrel lengths, buttstocks, and calibers in the field with nothing fancier than an Allen wrench.

The SIG MCX Rattler eschews a forward assist device and sports a bilateral safety and magazine release.

While 5.56mm barrels are in the pipeline, the most common variant of the Rattler pushes .300BLK.300BLK allows the option of either stupid-quiet subsonic loads for maximum stealth or supersonic rounds for those times when you need a little more downrange horsepower. The 5.5-inch barrel makes the MCX Rattler incredibly compact. SIG engineering and the .300BLK chambering make it unnaturally versatile.

The muzzle of the MCX Rattler is threaded 5/8×24 for a .30-caliber sound suppressor. In addition to just about everything else, SIG makes these, too. Their SIG SRD762 is the top of the line.

The SRD762 is a novel tubeless welded can built from Inconel and sporting wrench flats on the front. There are also some truly scary-looking teeth should you feel the need to set the gun against a door facing or prod some recalcitrant miscreant. This can threads directly onto the gun’s muzzle and secures in place via a Taper-Lok shoulder for minimal POI (Point of Impact) shift. It weighs about a pound and runs like a champ.

The two-position gas system on the MCX Rattler is easily adjusted with either the tip of a bullet or your finger. One setting is for subsonic ammo. The other is for the fast stuff.


Both guns sport an essentially identical manual of arms. Each weapon employs the classic Stoner-designed T-handle for charging and offers similar controls. Each magazine well is flared slightly for fast reloads, and the guns both have plenty of rail space for accessories. Both designs also keep their recoil systems inside the receivers, negating the need for a buffer tube out the back.

They are modular designs that allow easily interchangeable forearms, buttstocks, and barrels. We gun nerds like to accessorize our modern tactical weapons more vigorously than our young daughters might individualize their Barbie collection. The MPX and MCX Rattler are comparably versatile in this regard. Neither gun includes forward assist device.

They both use the same remarkable sliding Pistol Stabilizing Brace. These contrivances mount a firm rubber arm brace on the end of a pair of steel struts akin to those of the M3 Grease Gun. A top-mounted pushbutton releases the device for extension or stowage. They are both comparably comfortable.


The MCX Rattler uses standard ubiquitous M4 magazines, while the MPX employs a proprietary translucent polymer version a bit bulkier than those of an MP5. M4 mags are cheaper and easier to stockpile, but the MPX boxes are smaller and tidier to pack, albeit in proprietary mag pouches. Both magazines include a substantial curve that helps you get them oriented in the dark.

The Rattler is a sub-variant of the superlative SIG MCX rifle series. This gun can be configured in literally hundreds of different combinations to address specific missions and circumstances. Unlike the MPX, it lacks a right-sided bolt catch. By contrast, the MPX is a unique small-framed design. The MPX gas system is fixed. That of the MCX Rattler is adjustable.


Pick your poison. Both guns take corners like a Bugatti while running easily indoors or within a vehicle. The MCX Rattler is perhaps a bit quieter with subsonic ammo and hits harder with the spunky stuff. However, it’s tough to beat Herr Luger’s 9mm for cheap high-volume training.

Both weapons are unabashedly expensive, but you get what you pay for. Superlative ergonomics, perfect execution, and brand cred that are both hard-won and comparably justified come at a cost. However, if you want to run the apex predator as your primary home defense arm, one of these two brothers is it.

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About the author: Will Dabbs A native of the Mississippi Delta, Will is a mechanical engineer who flew UH1H, OH58A/C, CH47D, and AH1S aircraft as an Army Aviator. He has parachuted out of perfectly good airplanes at 3 o’clock in the morning and summited Mount McKinley, Alaska, six times…always at the controls of an Army helicopter, which is the only way sensible folk climb mountains. Major Dabbs eventually resigned his commission in favor of medical school where he delivered 60 babies and occasionally wrung human blood out of his socks. Will works in his own urgent care clinic, shares a business build-ing precision rifles and sound suppressors, and has written for the gun press since 1989. He is married to his high school sweetheart, has three awesome adult children, and teaches Sunday School. Turn-ons include vintage German machineguns, flying his sexy-cool RV6A airplane, Count Chocula cereal, and the movie “Aliens.”

{ 3 comments… add one }
  • LPD256 March 5, 2018, 12:13 pm

    I have a Sig MPX SBR with an Omega 9k suppressor. More grins received than from anything else in the arsenal. As an SBR it has NFA travel restrictions. So my travel trunk gun is a Sig PM400 pistol in 5.56. 11.5 inch barrel is a noise maker. May switch to a 300 BLK upper with a can. But as a pistol I can travel anywhere. Dr Dabbs if you need an assistant, give me a call. Haha…

  • Mark March 5, 2018, 9:56 am

    Well I do own a sig 9mm pistol and AR15, I opted to get a CZ Scorpion half the price and one can buy lots of aftermarket parts for it and still be under cost of a Sig. And I runs perfect every time! On and type of fuel 🙂

  • Cyrus March 5, 2018, 7:17 am

    “The addition of a Pistol Stabilizing Brace makes it the ultimate home defense weapon” I’m gonna go ahead and have to disagree with this. FWIW the Remington 870 or Mossberg Persuader is the ultimate Home Defense weapon with my 45 tucked into my belt.

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