EXCEEDING THE STANDARD
Sig Sauer MCX SBR: Designed Ground-up for Suppressed 300 BLK
SIG Sauer’s modular-platform MCX is engineered to redefine out-of-the-box shooting performance.
It’s easy to see how modern rifle designers, manufacturers and shooters alike have embraced the concept of modularity. This ease of parts-interchangeability is delivering us from traditional platforms, whose customization and modification required complicated, laborious gunsmithing work, to completely modular designs such as the AR-15 and its contemporaries.
Being able to take an AR-15 upper from company X and slap in a barrel from company Y then install it on a lower from company Z is certainly a convenient way to go. With a market full of in-spec components, the sky’s the limit when it comes to customizability options. Even if you have a rifle cobbled together with parts from multiple manufacturers, you’ll know that you can reasonably assume it’s safe to fire and may even be as accurate as one made from a single manufacturer.
But in a world where mismatched “Frankenrifles” have seemingly become the norm, we may not immediately realize that the benefit of the modularity of rifle components, however ingenious the concept, might not be perfectly executed on each and every build.
Why does one rifle shoot more smoothly or accurately than another? Some will point out that they tuned their adjustable gas block or buffer. Others will say it’s their special recipe for their ammo reloads. When it comes down to it, it’s the intangibles that make it difficult to really know why. When you’re making a stew, all the ingredients allow it work—or, in some cases, not work.
Complete Systems Provider
SIG Sauer is a name that needs no introduction in the firearms industry. The esteemed manufacturer thought long and hard about modularity and what it meant to shooters when it developed its newest and arguably most progressive rifle to date. The designers realized that only through meticulous engineering and precision manufacturing could the true benefit of modularity be achieved.
The SIG Sauer MCX isn’t just another AR variant or an AR that’s been updated or tweaked. It’s a completely new ground-up design that reflects decades of collective hands-on experience of shooters of all types. Before we delve into the intricacies of the MCX, let’s reveal what SIG has been up to lately.
If you haven’t noticed by now, SIG has greatly expanded its capabilities and offerings over the past few years. Already well known for finely crafted pistols and rifles, SIG is now also producing its own sound suppressors, optics and even ammunition.
Unlike other big-time conglomerates, all divisions at SIG work hand in hand to make sure their products are designed to work in conjunction with one another. If you are looking for a complete weapons system that includes everything from the rifle and suppressor straight through to optics and ammunition, look no further than the MCX.
Like others, when we first laid eyes on the MCX it was with a mixture of love at first sight as well as, “Oh, that’s just another AR.” Read on to find out exactly how wrong we were about that last sentiment.
The complete MCX SBR system shown here is a culmination of multiple divisions and hundreds of cooperative man-hours. At first glance, you’ll notice the MCX SBR rifle itself as well as the SRD762TI suppressor. Up top, you’ll see the SIG Romeo red dot optic, but the SIG ammo isn’t immediately apparent.
What is impressive is that every element of the MCX was designed to achieve its mission of silence, light weight, compact size and hard-hitting accuracy out to 300 meters.
The MCX looks similar to an AR-15 because SIG wanted to create a rifle with Ar-style controls since so many shooters are already familiar and comfortable with them. No need to reinvent the wheel, so to speak. An added bonus is that aftermarket AR parts such as pistol grips, safety selectors, magazines and triggers are all compatible.
The MCX’S lower receiver is machined from aluminum alloy and features a flared magwell and an oversized, integrated trigger guard and houses an Ar-style trigger assembly. The lower features ambidextrous controls, so both your strong and support hands can operate the gun without any extra effort. Its magazine release is larger than that of an AR and appears on both sides of the receiver.
Another ambidextrous control is the safety selector switch, whose levers reside on either side of the lower. However, we noticed that it lacked a bolt catch release on the right side to make it fully ambidextrous. It’s not a big deal, but is worth noting for those who absolutely need dual-sided controls. What it does have are two quick-detach (QD) sling mount points mirrored at its rear end that are great for attaching single-point slings.
An advantage the MCX has over traditional
ARS is that its buttstock can be folded tightly against its left side. Unlike an AR, there’s no buffer tube to worry about. SIG offers a variety of different folding and retractable stocks that are painless to swap thanks to a quick-change rail system. It even offers an adapter that accepts an AR buffer tube so you can fit any of your favorite aftermarket stocks.
A telescoping and folding 3-position stock is now available and comes standard. The lowprofile skeletonized stock attached to our test SBR is optional. Both stocks are light in weight, slim in profile, and contain QD sling mounts on both sides.
The MCX SBR featured here has a 9-inch barrel and is chambered in .300 AAC Blackout (300 BLK). The MCX is also available in 16inch barrel length carbine, 11.5-inch SBR, 11.5-inch pistol and 9-inch pistol models with different caliber choices. If you don’t know which one to choose, you’ll be glad to know that you might not have to.
The MCX’S upper receiver is convertible for caliber and barrel length. You don’t need to be a gunsmith to convert it, either.
SIG’S engineers made sure that anyone, mechanically inclined or not, can perform the conversion reliably and safely. By removing just two screws, you can remove and replace the barrel assembly and handguard with different units.
The MCX operates on a short-stroke gas piston system and has a two-position gas valve lever to optimize it for suppressed and non-suppressed fire. Gas piston operation is a proven system renowned for its reliability. The rifle benefits from retaining its operating system in its upper receiver, meaning there’s no need for a buffer tube and recoil spring as in an AR. This helps keeps the rifle short and allows for a folding stock.
The monolithic and free-floating barrel design of the upper receiver allows the rifle to be rigid and accurate. A full-length Picatinny rail runs across its top, ready for optics and accessories mounting. Our tester came equipped with a set of SIG’S flip-up iron sights for backup sighting. As mentioned previously, the aluminum-alloy handguard can be interchanged with longer lengths to accommodate longer barrels, as can even lighter carbon-fiber handguards.
You’ll find Keymod mounting points at the 3, 6 and 9 o’clock positions on the handguards. Robby Johnson, Government Program Manager at SIG Sauer, explains: “We decided to go with the Keymod handguard system because it’s a proven design. With Keymod we have a chamfered mounting surface, so our straight pull strength is upwards of 280 pounds.”
Realizing that general use can cause extra wear to the upper receiver in critical and common wear areas, SIG implemented steel inserts in the upper that can be user-replaced as needed to increase the longevity of its rifle.
To push its capabilities even further, the MCX’S upper receiver is fully compatible
with mil-spec AR-15 lowers. How awesome is that? If you wish to install one of SIG’S folding or collapsible stocks on an AR lower to use with the MCX’S upper, the manufacturer offers a conversion kit that requires only three simple tools and a few minutes to install. The removal of the stock AR buffer tube is required, however.
You could say that the MCX was born to shoot Blackout ammo, but that doesn’t mean it’s completely set in its ways. Not one to turn down ammo to munch on, the MCX can be converted on the fly to feed 5.56x45mm and 7.62x39mm cartridges. This same conversion process also allows you to change barrel lengths.
Barrel and caliber conversions are not new to modular rifles, but what sets the MCX apart from the rest is that its conversion process is designed to take only a minute and a half. We tried it, and even without being familiar with the process, we were able to get it done in the same amount of time.
The MCX was designed to meet the U.S. Department of Defense’s requirement for a compact rifle whose focus is on sound signature reduction as well as combat effectiveness out to 300 meters. With that in mind, SIG specifically developed the MCX to run suppressed on 300 BLK caliber ammunition. The Blackout round was optimized to take down targets at midrange distances and run through suppressors efficiently.
Most suppressor companies do not make firearms. To that end, they create silencers that are made to fit any number of guns. Specific issues for each individual end user such as pressure, heat, and even caliber usage can amount to be a guessing game. SIG’S big advantage in this area is that not only do they make the guns, but also suppressors that they can tailor to each application. This is a cornerstone of what makes the MCX such a complete system. The rifle and suppressor were developed to work in total harmony.
Because SIG’S primary goal for the MCX was to run as silently as possible, it was primarily engineered to run a suppressor right out of the box, unlike many other rifles with add-on suppressors. A challenge of mounting silencers to firearms is retaining unsuppressed accuracy. Due to manufacturing processes and suppressor design, SIG
“The MCX SBR is a completely new ground-up design that reflects the collective hands-on experience of shooters of all types.”
has been able to attain better accuracy with less point-of-impact shift from the MCX and its silencer. This results in the MCX running just as well suppressed or un-suppressed in terms of control, accuracy and reliability.
The MCX is optimized for both subsonic and supersonic versions of 300 BLK caliber ammunition. This allows supersonic ammunition to retain accuracy and lethality at 300 meters even when suppressed. Incredibly, when subsonic Blackout is fired through a suitably configured MCX, it can give you the equivalent sound of a silenced .22 caliber round. Goodbye, sweaty earmuffs!
The SRD762TI silencer we tested is made of grade 5 titanium and fitted directly to the rifle’s barrel threads. It weighs just over a pound and measures a tad over nine inches long. Thanks to a unique baffle design and advanced robotic welding techniques, SIG was able to greatly reduce the silencer’s weight by eliminating its outer tube by using its own baffles as its tube. This resulted in not only a lighter silencer, but also a gain in internal volume and reduced internal pressure, which helps increase silencer durability.
Boldly encroaching onto Aimpoint and Eotech territory, SIG really did set out to make sure that its rifles could be completely outfitted with SIG Sauer–developed accessories. To that end, we got to check out its Romeo4 red dot. Similar in size and shape to an Aimpoint Micro-series optic, the Romeo4 differs in that it is activated with rubberized push buttons on its top surface and is switchable between a 2 MOA dot and an Eotech style, 65 MOA circle dot reticle. Like other red dots, it promises unlimited eye relief and is parallax free.
The Romeo4’s body is machined from aluminum and has a listed battery life of 50,000+ continuous hours running on a single CR2032 battery. We didn’t have a chance to try it, but we would be interested in seeing how the Romeo4 would fare in a longevity and durability test. Several Romeo4 models are offered, the newest being the Romeo4s, which is equipped with a solar cell that can increase its battery life to 100,000 hours.
At the Range
We headed to the range with a certain amount of excitement, as we haven’t had
“engineered to run a suppressor right out of the box.”
the chance to shoot through SIG’S silencers before. Shortly after arriving and setting up a series of AR500 steel gongs at differing ranges, we went to work by loading up magazines full of SIG’S Elite Performance Match ammunition.
Using a mixture of U.S.G.I. and Magpul PMAG magazines, we loaded both SIG Elite 300
BLK subsonic rounds and their supersonic counterparts. The subsonics feature 220-grain Sierra Match King projectiles while the supersonics are loaded with 125-grain Sierra Match King bullets. Yes, fancy stuff—we are spoiled at times. We started with the subsonic rounds.
Unloaded, the MCX SBR weighed in at less than six pounds. With the added optic and suppressor, it still felt light and very well balanced. You would think that a suppressor on one end and a thin buttstock on the other would mean it would want to take a nosedive, but that wasn't the case. The rifle was well balanced, with just a smidgen of the balance felt forward of the pistol grip. Because of its AR control layout, we instantly felt at home with it—except for the folding stock, which took some getting used to.
For our first string of fire, we decided to go sans ear pro. The subsonic rounds are made for low noise levels, and we wanted to see just how quiet they are. Clack, ding! Clack, ding! That’s all we heard. It was a surprise: The sound of the bullets hitting the steel managed to sting our ears, but not the shots fired from the MCX. We actually had to shoot into the dirt to clearly hear the sound of the gun, as the ringing of steel had drowned it out. No kidding. If SIG set out to make a quiet rifle, it certainly was achieved.
“We’re willing to bet that no amount of Franken-building will get you closer to the level of Sig Sauer’s design, engineering, build quality and shooting sensation.”
The MCX was a pleasure to shoot and handle. Its trigger was clean and not at all gritty. Its pull measured a bit over 7 pounds on our Lyman trigger-pull gauge, which isn’t bad for a stock trigger. That said, we think an aftermarket trigger would be an outstanding addition to this rifle.
Naturally, the suppressor got really hot after we fired a few hundred rounds through it. The MCX we tested had the shorter SBR handguard attached, so we were wary of getting burned by the silencer. Gloves on! We suspect if we installed the longer handguard that partially covers the suppressor, it would better protect us from incidental burns—of both person and property.
Unfortunately, we didn’t have an opportunity to shoot to 300 meters on this particular range day, so for the supersonic rounds, we had to settle for 100 yards. Naturally, the 6-inch steel gongs were no match for the 125-grain Sierra Match Kings we launched at them. Even suppressed, we noticed that the hits were all point of aim, point of impact.
The day started sunny and very bright, so we had to crank the reticle brightness to a higher level on the Romeo4, but not to the point of maxing it out. The reticle was switched between shooters from the plain 2 MOA dot to the 65 MOA circle dot depending on personal preference. The red-colored reticle was easy to pick up no matter how bright or dark the conditions.
We’re willing to bet that no amount of Franken-building will get you to the level of
SIG Sauer’s design, engineering, build quality and shooting sensation. The MCX SBR is more than just a rifle: It is the basis of a complete system when combined with SIG Sauer designed and manufactured accessories such as the outstanding SRD762TI silencer. It really is a tough combination to beat.
Each of the four shooters who fielded the MCX SBR with the SRD762TI that range day claimed it would be their next rifle and suppressor combo. In this line of work, we are fortunate enough to shoot a lot of rifles, so that’s not a statement to be taken lightly. SIG Sauer went above and beyond with the design, engineering and execution of the MCX SBR, and we believe that even the most discriminating of shooters will enjoy this rifle.
The MCX is available in 16-inch barrel length carbine, 11.5inch SBR, 11.5-inch pistol and 9-inch pistol models with different caliber choices.
The MCX lower receiver features ambidextrous controls, so both your strong and support hands can operate the gun without any extra effort.
One added MCX bonus is that aftermarket AR parts like pistol grips, safety selectors, magazines and triggers are all compatible with the SIG Sauer system.
The MCX was a pleasure to shoot and handle—clean, never gritty. Trigger pull measured a bit over 7 pounds, which isn't bad at all for a stock assembly.