Breaking Away from the Norm: The Modular/Adaptable SIG SAUER MCX

By Todd Burgreen

SIG SAUER, Inc. has evolved into a recognized industry leader in the development and manufacturing of rifles, SMGs, handguns, optics, ammunition, suppressors etc. SIG SAUER has entered the rifle market in force over the last several years. SIG SAUER definitely now has “skin” in the rifle game, with numerous models and calibers in its product line-up.

Of late, the most attention seems to have been paid to “improving” the AR platform, either via developing piston-driven ARs or caliber expansion beyond 5.56mm. This leads us to SIG SAUER’s latest rifle offering, which embodies both: the MCX. The MCX represents the latest approach to rifle methodology in terms of modularity without sacrificing rugged reliability. While sharing similar aesthetics to the venerable AR, the MCX is a new approach blending adaptability of caliber and configuration.

The MCX spawned from a SOCOM request to develop a lightweight, compact multi-caliber rifle that was intended to be operated suppressed. Based on this, it is not surprising that the MCX’s initial chambering was the .300BLK, with the 5.56mm (both evaluated herein) and 7.62x39mm quickly following. Typical of the Swiss/German engineering background of the company, the MCX design was not hastily introduced in a knee-jerk fashion. The process took over three years before SIG SAUER was ready to introduce MCX to the market by designing a self-regulating short-stroke piston.

The SIG SAUER designers needed to meet a 50,000-round count criterion to satisfy the initial solicitation that brought the MCX to life. This should allay any concerns over its modularity affecting durability in terms of wear and “loosening” up with use. Obviously, quality materials are a must, along with a full understanding of high-wear parts on the rifle. SIG has designed the MCX with certain key wear components upgraded to steel versus aluminum; these parts are also easily replaceable. For example, the cam path insert and feed ramp insert. The charging handle latches move over steel pins as opposed to aluminum pins. Barrels for the SIG SAUER MCX are hammer forged and receive a nitride treatment for increased barrel life. The MCX utilizes a fully locked and closed rotating bolt system, minimizing any chance of out of battery failure/malfunction.

The caliber, barrel length, forend, buttstock and suppressor on the SIG SAUER MCX can all be changed based on user desire. The modular nature of the SIG SAUER MCX is not a gimmick or applied to only a handful of custom rifles. The MCX is a fully vetted production rifle backed up by one of the most reputable firearms companies in the world. SIG SAUER’s decision to go the extra mile in designing and manufacturing the MCX to military-like specifications establishes a baseline of quality that separates the SIG MCX from other rifles.

The MCX is capable of accommodating all three cartridges mentioned above, thanks to the ability to quickly switch barrels and bolts accordingly. The 7.62x39mm modification requires the lower receiver to be switched out as well, to work with AK magazines. This article takes advantage of barrel kits becoming available to the civilian market allowing for full exploration of the MCX concept versus only a single caliber review—negating the MCX advantage. The key part of the MCX’s modularity/adaptability is the capability to switch calibers without sacrificing performance.

The MCX operating controls and basic ergonomics are similar to those of the ubiquitous AR15—an important consideration for training/orientation purposes. The AR-like ambidextrous magazine and bolt release, along with the centrally located non-reciprocating charging handle, will be instantly familiar to any AR user. A flat-top upper allows for any AR-type sighting system. This AR-centric theme is reinforced by using an AR-type fire control system. However, the bolt carrier group is different to an AR’s. This stemmed from the initial user’s request to use a folding stock in lieu of a typical AR buffer tube set-up. SIG installed dual recoil springs above the bolt carrier group. Due to the recoil spring placement, the charging handle sits slightly higher on the MCX compared to an AR. Not only do the dual recoil springs enable the folding stock, they also offer the benefits in terms of making the recoil impulse smoother/softer, eliminating the buffer tube wear associated with AR piston-driven rifles and increasing overall reliability/durability.

The SIG MCX can be viewed as a fresh design since the field became dominated by the AK and AR. The SIG MCX represents a new age of rifle modularity. Changing the caliber between 5.56mm and .300BLK is a simple matter with the MCX. The fact that the 5.56mm and .300BLK share the same magazine and bolt group is the foundation for this. Removing the forend exposes two captive T27 Torx bolts. Loosening these allows the barrel and gas piston to be removed. The new barrel and gas piston are then installed with the two T27 Torx bolts tightened to 60 inch-pounds. The whole process is truly as simple as it reads.

The MCX gas port locations change depending on the caliber chosen. Much of the SIG SAUER MCX development focused on finding a placement of the gas ports to optimize reliability. SIG SAUER chose to go with a more complete approach with the MCX. The MCX features an adjustable gas regulator, with the first position for normal operation and the second for using a suppressor. As stated previously, the MCX was designed from the beginning to accommodate suppressor use: an obvious reflection of its adaptation to current trends in fighting rifles. The MCX’s short-stroke gas piston’s advantage is that heat, soot and carbon from propellant combustion are not routed into the bolt or chamber, keeping these critical areas cooler and cleaner for greater reliability. This is particularly important given the increasing use of suppressors.

A SIG SAUER SRD762-QD suppressor was chosen for use with the MCX combo calibers. It was as simple as installing a SIG Taper-Lok muzzle device adapter on each of the MCX barrels. It was decided to use the SRD762-QD on both to keep things streamlined. Basically, if the bullet diameter is .30 caliber or less, the SRD762-QD can be used—perfect for the adaptable/modular MCX .300BLK and 5.56mm barrels. The SIG SAUER Taper-Lok is not only an ingenious mounting system for the suppressor body but also an effective flash hider or muzzle device in its own right.

The SIG SAUER theme was continued with the decision to mount a SIG SAUER TANGO6 1-6x24mm optic. The TANGO6 offers a 1x illuminated reticle setting for quick target acquisition at close range with both eyes open. A quick turn of the knob to 6x enables longer precision shots. The SIG SAUER TANGO6 is loaded with high-end features, such as an adjustable illuminated MOA reticle, extra-low dispersion glass combined with high transmittance glass for outstanding light transmission and clarity, along with resettable lockable and zero stop turrets. A reticle with multiple hashmarks is preferred with a caliber such as .300BLK, so that both subsonic and supersonic ammunition hold points can be established. This is further supported by the MCX also having to accommodate 5.56mm chambering. Once sighted in, a user can take note of where each load strikes relative to one another and adjust accordingly—either via scope turret knobs or with reticle hashmarks depending on the situation.

Ammunition tested with the SIG MCX was a combination of multiple 5.56mm/.223Rem loads from Black Hills Ammunition, Hornady and Federal loads. No load tested produced greater than 2.25-inch groups at 100 yards. Premium loads, typified by the Federal Match 69-grain Match, punched five rounds into a 1.5-inch group. Remember, the MCX is a fighting rifle—not a match target rifle affair—making this performance even more impressive. The .300BLK ammunition tested with the SIG MCX comprised the Hornady supersonic 125-grain HP, Hornady 208-grain AMAX, SIG SAUER Elite 125-grain and 220-grain Match subsonic and Black Hills Ammunition 220-grain OTM.

What distinguishes the .300BLK is the ability to access standard supersonic rounds for typical hunting or longer-range engagements superior to 5.56mm while maintaining the trump card of subsonic ammunition for more discreet specialized work. Similar to the SIG MCX, the .300BLK was created in response to a US special operation military forces request. Literature illuminates their goal with the .300BLK as being the ability to launch .30 caliber projectiles from the AR platform using existing 5.56mm magazines without a reduction in magazine capacity or reliable functioning. Another notable characteristic of the .300BLK is its compatibility with the AR standard bolt; thus, only a barrel change is necessary. According to anecdotal information, standard-velocity .300BLK 115–125-grain ammunition matches the ballistics of the 7.62x39mm AK and eclipses 5.56mm both in ballistics and terminal punch. At 300 meters, the .300BLK has approximately 17 percent more energy than the 7.62x39mm. When fired from a 9-inch barrel, the .300BLK has the same muzzle energy as 5.56mm ammunition fired from an M4 with a 14.5-inch barrel; as the range increases, its energy then surpasses that of the 5.56mm.

The Hornady, SIG SAUER and Black Hills .300BLK loads were chronographed. The supersonic loads clocked on average between 2210 and 2395 feet per second from the MCX’s 16-inch barrel, with the subsonic loads measuring 990–1005 feet per second. The accuracy from the .300BLK barrel was a pleasant surprise. Previous experience with other .300BLK rifles had generated less than stellar consistency, with certain loads favored greatly over others. This was not the case with the SIG SAUER MCX. No load tested, whether supersonic or subsonic, produced a dispersion greater than 1.5 inches at 100 yards after firing three 5-round groups. This accuracy level justifies considering leaving a magnified optic, such as the versatile SIG SAUER TANGO6 1-6x, mounted on the MCX.

Several magazines’ worth of ammunition was spent engaging plate racks and man-sized steel targets with the SIG SAUER MCX, changing calibers periodically. Drills quickly moved past stand-and-deliver drills to more dynamic drills involving movement, magazine reloads and firing from behind cover. The recoil impulse of the .300BLK is similar to that of a 5.56mm. The SIG SRD762-QRD suppressor was also incorporated into the range evaluations. It was decided to concentrate on using the SIG MCX in training scenarios involving team tactics and patrolling to contact through Echo Valley Training Center’s (EVTC) 360 and “Jungle Walk” ranges. This allowed the SIG SAUER to shine in terms of potent firepower and combat accuracy. Firing from unorthodox positions while working around range vehicles showed why the 6-pound MCX combines so effectively with the enhanced firepower of the .300BLK.

Interestingly, the .300BLK subsonic loads had no issue cycling the rifle, even when firing without a suppressor attached. Not every .300BLK rifle on the market shares this characteristic. The advantage of having a .300BLK rifle like the SIG MCX functioning with subsonic loads unsuppressed is that a user can be confident of a functioning weapon no matter the ammunition in use.

The minimalist nature of the SIG folding skeleton stock caused initial skepticism as to ergonomics and effectiveness. This was quickly dispelled once the shooting started. The folding stock proved rock-solid and provided excellent cheek weld for sighting with any optics; kudos to the SIG SAUER design team for this. The MCX lived up to the task of being a lightweight, fast-handling rifle. The light and handy MCX is what individuals will choose to work with environments represented by these ranges. Over 500 rounds each of 5.56mm and .300BLK were fired for this T&E. The piston-driven MCX proved utterly reliable, with only minimal effort given to wipe down the bolt carrier group and lubricate sporadically.

One nuance noticed during MCX manipulation during magazine changes was that the charging handle is best operated with two fingers, so as to keep the pull to the rear linear and not off to the side. One could feel binding when using only one side of the charging handle. This is most likely due to the dual springs on top of the bolt carrier compressing unevenly when using only one hand. Even with two fingers, the charging handle manipulation on the MCX is definitely stiffer than on your typical AR.

SIG SAUER’s thought process with the MCX was to create a lightweight, simple-to-operate rifle that was eminently adaptable to user needs. The flexibility to chamber it in .300BLK is a nod to realism, acknowledging that 5.56mm is no longer the only viable chambering option for entities with the option/motivation to choose otherwise. All MCX features are intended to maximize effectiveness during a fight or realistic training on the range. The key component in a fighting rifle is reliability. No matter how accurate the rifle or powerful its chambering, if it does not work 100% of the time it is a liability. Selection of a fighting rifle is as personal as it gets. The SIG MCX is intended for serious practitioners who plan on using it for patrolling, training or defense. A return to assault rifle basics, such as prioritizing lightness, great handling and potent firepower, is often the answer. SIG SAUER offers such a platform with its MCX.


Black Hills Ammunition
Echo Valley Training Center
Hornady Manufacturing

Hazard 4’s New Slingpacks – Comfortable, Practical and Rugged

Nothing is as individualistic as deciding how to carry immediate action items, such as a handgun, weapon magazines (handgun and rifle), a medical IFAK, a radio and whatever else is deemed a necessity in high-risk environments. Factors such as accessibility, adaptability, fit, weight to mobility ratio, retention and the most effective use of limited real estate on an operator’s body all come into play in the decision-making process. Let’s face it, the world is only becoming a more dangerous place—not only overseas but also here in the U.S.

A company helping to equip not only our military, law enforcement and private security contractors (PSC), not to forget civilians, is Hazard 4®. Hazard 4’s parent company is Civilian Lab. Civilian Lab has a number of years’ experience manufacturing top-quality outdoor adventure, extreme sport and travel gear in innovative configurations and form factors. It’s had countless users asking over those years for tactical and professional versions of that gear.

The Hazard 4 Plan B Sling Pack and Smuggler have been in use supporting various article projects for the last several months. The convenience with which they can be adapted to carry multiple weapons and ancillary gear (ammunition, optics, suppressors) is much appreciated. The Plan B is part of the Hazard 4 Evac series of sling packs. Slim shaped, for fast maneuvering in crowds, they can be stored in vehicles/lockers and are quick to take on or off. The Hazard 4 is actually comfortable to wear. The main padded strap is cocked at either the right or left lower corner, so the pad aligns ergonomically in the correct body-hugging direction. There is no slack or gapping away from the body, as is typical with similar single-shoulder packs. The bag can be rotated to the chest for on-the-go access, and all pockets are designed to face the user in this mode on either the right or left side. This means the user can go from wearing the pack on his back to driving a vehicle with it on his chest in just a few seconds. The Plan B’s one-strap design also makes shouldering a long gun natural.

The Plan B’s big brother, Smuggler Pack, has evolved into one of my favorite weapon transport cases. The Smuggler is a large Evac series sling pack specifically designed to accommodate carbines up to AK47/AR length. However, the Smuggler is designed so that users do not feel their items are “jammed” in. I found it easy to accommodate an AR pistol and compact shotgun with no issues. Shooters can transport their rifles with a magazine inserted and/or optics mounted. Additional external pockets can carry magazines, cleaning kits, extra parts and everything you need to transport your work gun or haul around urban gear. A folded padded sleeve is included with the Smuggler. It can be used as padded support for any items you may wish to place inside the compartment, or it can be used to hold a rifle inside. This means you can place a rifle inside the folding sleeve itself (in addition to the rifle ties behind the fold sleeve) to provide a little cushioning for it. The folding sleeve can also be taken out of the bag and used as a shooting mat if you need it.

A visit to Hazard 4’s well-designed website is a must to fully understand the thought process behind their many impressive products.

Hazard 4®

This article first appeared in Small Arms Review V21N7 (September 2017)
and was posted online on July 21, 2017


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