Sig Sauer MCX

Sig Sauer MCX

Tactical Air Rifles and Optics Part 1

By Dennis Adler

Designed by Sig Sauer for military and law enforcement, the MCX is one of the latest designs for a multi-platform weapon system. The Sig Sauer MCX CO2 model is as close in appearance and basic function as the 5.56mm rifles. The MCX is shown with a Sig Sauer Bravo4 optical battle sight (used on the cartridge models). A Sig Sauer P226 ASP air pistol (holstered) is shown with a UTG tactical vest, tactical gloves and Surefire 2211. The Surefire combines the Luminox watch used by Navy SEALS and other military units with a 300 lumen tactical light.

Sig Sauer MCX Part 2

Sig Sauer MCX Part 3 

This model of the Sig Sauer MCX tactical air rifle is based on the military version with noise suppressor and solid shoulder stock (which is used to house the 88 gram CO2 cylinder). To match it with the actual 5.56mm military version I have also equipped it with the Sig Sauer Bravo4 4x30mm Battle Sight. The Sig Sauer optic is the same used by military and law enforcement and costs considerably more than the air rifle it is mounted on, but if you have the MPX civilian version, the Bravo4 is absolutely the first choice for optics, as it was built for the MPX and MCX air rifles. Throughout this series of articles we will also be reviewing other optics designed for CO2-powered air rifles, but for this first installment I decided to show just how authentic this new Sig Sauer CO2 model can be, and look.

The Sig Sauer MCX CO2 model has the full length 21-inch rifled barrel surrounded by a faux suppressor and KeyMod-style hand guard.

When I say “new” the Sig Sauer MPX and MCX are among the latest military rifles, having been introduced late in 2014. Selective fire versions were developed for military and law enforcement, as well as semi-auto civilian models. The MPX and MCX were designed to be the most modern and adaptable (modular) military rifles available; light in weight at around 6 pounds (the CO2 version comes in at 6 pounds, 10.5 ounces with the suppressor shrouded 21-inch barrel), and has the same lean profile for ease of balance and quick handling in close quarters. The MPX has a 16-inch barrel making it a CO2 version of the Sig Sauer SBR (Short Barrel Rifle) model.

On the right side of the CO2 model, all of the features of the 5.56mm model are duplicated but only the magazine release and ambidextrous safety are functional features. The rest are meticulously detailed non-functioning controls that serve no purpose in operating the CO2 model.

If there was one end result Sig Sauer was seeking with its design for the MPX and MCX, it was a modern day version of its legendary (and still in use) MP5 versions. The rifles were developed for use by Spec Ops and offered to U.S. Special Forces. They were first chambered in .300 Blackout, then in 7.62x39mm and the 5.56x45mm NATO round used in the M4A1 (among other battle rifles in use today by U.S. forces). The U.S. military has not yet adopted the MCX (currently that role is filled by Heckler & Koch’s HK416) and there are still on going developmental changes, including modifications to the bolt carrier group on all current models (a mandatory recall and replacement) and for new production models as a safety upgrade. One can recall the many issues that plagued the M16 when it was first introduced more than 50 years ago, and today it is the foundation for the majority of military and law enforcement rifles, including the Sig Sauer. The HK MCX and MPX are much further along in just their first couple of years than the AR platform was after a decade.

Left side features designed into the receiver include non-functioning bolt and magazine releases. The ambidextrous safety is the only operating control on this side of the airgun.

In operation the cartridge-firing MCX and MPX are modular AR hybrids with a short-stroke gas piston design that eliminates the need for a buffer and gas tube; in their place Sig uses a compact recoil system contained completely within the upper receiver, making the rifles more compact with a lightweight tubular stock that can be folded alongside the receiver. For the CO2 versions the Sig design creates a simple, integrated shoulder stock tube to surround an 88 gram gas cylinder, which provides the air rifles with up to 700 fps velocities for 4.5mm lead pellets. This is combined with high-capacity 30-round magazines which operate on a unique rotary internal belt. The pellet magazines look like short (10-round) AR mags.

Externally, the airguns have very similar lines and use the same lightweight skeletonized KeyMod-style handguards. KeyMod handguards are designed with different inner diameters so that they can fit over barrels or sound suppressors as needed. The longer handguard design (as seen on the MCX) acts as a continuation of the one-piece top rail, giving you over 15 inches of accessory rail on the CO2 models. The KeyMod handguards will also accept a variety of accessories including the vertical foregrip that comes with the CO2 model, as well as mounting tactical lights and lasers. On the cartridge models the handguards are designed for quick removal and the Sig uppers can be quickly switched out for different barrel lengths, calibers, and accessories in the field. A bit much for a CO2 version to adopt, so the airguns are standard configurations of the two Sig models, the MPX and suppressed MCX (once again a visual not a functional feature on the CO2 model).

As real looking as it gets, the new Sig Sauer MCX can be equipped with the same accessories as the cartridge-firing models, including the Sig Sauer Bravo4 optical battle sight.

On the cartridge models the fire controls are ambidextrous; safety selector, extended magazine release buttons. and charging handle. On the MCX model, the bolt release is only available on one side of the gun, whereas it is ambidextrous on the MPX. All of this is nice to know but little translates to the air rifle as all of the controls, except for the ambidextrous safety, charging handle, and right side magazine release are functional, the rest are meticulously molded into the receiver and magazine well to look 100 percent real, but not function. Other inert features are the ejection port cover, forward assist and disassembly pins. The flip up front and rear BUIS are fully adjustable and more than adequate for the range of the CO2 model, however, it is optics that really make this new Sig Sauer 88 gram CO2 model perform.

In Part 2 we will review the Sig’s unique belt-fed pellet magazine, explore the Sig Sauer Bravo4 on the CO2 model, as well as other more affordable optics that work well with the MCX platform.

6 thoughts on “Sig Sauer MCX

  1. A very impressive replica. I’m still undecided though about whether to buy an MCX or MPX. I thought is might be worth while to wait and give SIG time to fix any problems found in the first couple of years after releasing the MCX and MPX. I’ve also hesitated to buy in order to exercise some “fiscal restraint.”

    In this series on tactical air rifles, will you also be reviewing the Daisy Winchester MP4? Or have you reviewed it before in the last few years?

    Here’s a related, albeit off-topic question about the new faux suppressor for the SIG Sauer P226 ASP pellet pistols. I know it doesn’t suppress the sound, but is there any data showing that it increases shot fps or improves shot accuracy? Even if the suppressor is just a smooth bore tube, perhaps its additional length gives the CO2 more barrel length to propel the pellet to higher fps. What do you think?


    • I won’t be reviewing the Winchester MP4 in this short series, just the Sig and Beretta and various types of optics. As for the P226 faux suppressor that will be coming up later this month, but you do raise an interesting point about velocity which we will address!


  2. I am not a fan of the 88/90 vi2 cartridges Expendive and other always available locally . Apparently you cannot leave them in for prolonged periods .The HPAC makes the Sig look like a paint ball gun . No thanks .Would like to see a dual 12 gm co2 adapter .This rifle would be better with fully functional not pressed in pseudo controls . Would like to see a larger version of the320 handgun mag in this riflecoupled with select fire capability .



    • Overall this is a pretty accurate looking air rifle and the straight shoulder stock looks like the stock on some of the select fire military versions, although they do fold, and this does not. Sig Sauer has always been unique in their approaches to design and the entire Sig Sauer ASP program of air pistols and rifles has kept non-functioning parts cosmetic. I do agree that if everything on both sides of MCX and MPX functioned, the CO2 models would be a little more exciting to handle, (particularly if you are left handed) but that would not change how well the gun works as is.


  3. I picked up the Sig 226 177 pellet pistol when it first came out. It is probably a stop gap pistol that will be discontinued . If the mag for the new 320 works , this first gen pistol is gone .Non functioning controls especially slide release, non adjustable rear sight .A big disappointment. Would have thought Sig would have upped the level of play with the rifle platform . I am lefty who shoots handguns lefty and rifles righty. Every serious shooter should practice with and be proficient with both hands, and for that reason ambi controls should be functional or omitted. A nice rifle that with a little more work , could be even better.


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