Sig Sauer MCX Part 2

Sig Sauer MCX Part 2

Tactical Air Rifles and Optics

By Dennis Adler

Built as a sport shooting pellet rifle and training gun, the Sig MCX ASP has the heft, balance, and handling of the 5.56mm model. The look of the airgun is based on the select fire military version with sound suppressor. The CO2 model is a semi-auto with accurately sized faux suppressor.

Sig Sauer MCX Part 3

Sig Sauer MCX Part 1

The Sig Sauer MCX ASP is a curious air rifle as there are many advantages to Sig’s ASP design, but the company has thus far continued to avoid superfluous features that serve no actual function on an air pistol or air rifle. This has been the case with the Sig Sauer P226 ASP models, and with the MCX and MPX CO2 versions of their tactical (sporting) rifles.

Defining the CO2 powered models

Even close up, the effort Sig Sauer put into crafting controls that look correct comes through. The ambidextrous safety (lower left) and magazine release are the only working parts on the right side of the upper and lower receiver. Also note that each air rifle bears its own proof mark and serial number. The caliber is highlighted in white, while the mandatory safety warning is discretely left neutral to blend into the side of the magazine well.

The Sig Sauer air rifles are semi-auto only (although as air rifles they could have been equipped with a selective fire mechanism), Sig’s goal, however, is to offer their CO2 models as realistic training guns, as well as for recreational use. Sig Sauer’s Airgun Division vice president and general manager, Joseph Huston explained that, “The industry has truly embraced our ASP air rifles and air pistols as excellent training tools when the cost of ammunition, lack of range time or other factors prevent people from training with their centerfire guns as much as they would like or feel they should.” In that respect, the use of inert components saves on the cost of redundant features or those that have no functional role in the airgun’s operation while not compromising the features of the Sig model, leaving only what is necessary for basic handling and firearms training. Personally, I think the closer an airgun intended for training is to its cartridge-firing counterpart the better (and I can use the Umarex S&W M&P 40 as a prime example), but taking the MCX at face value, it is exceptionally well built, and Sig puts its designs through a 15,000 round reliability test. Whether or not you agree with the non-functioning features, the design is sturdy and well built.

The Sig Sauer ASP MCX models have full Weaver/Picatinny top rails for mounting optics. From this perspective the new MCX looks like it is ready for the target range or the battlefield. The attention to the detail even in the non-functioning parts, like the forward assist look as though they are operational. Of course, on the airgun they serve no actual purpose. The top rail and KeyMod handguard, however, most certainly do, as does the convenience of the air rifle’s ambidextrous charging handle.

Why not selective fire?

To better understand Sig Sauer’s decision to make the airguns a copy of the semi-auto civilian models rather than the selective fire military version, you need to look at public perception and the debate about what separates a tactical rifle from a sporting rifle. As disparate as this discussion may seem for airguns, it is part of a fundamental debate that has gone on for decades and will likely never be resolved in the minds of many. But from a purely technical standpoint a tactical rifle (those used by military and law enforcement and not readily available to the public) have one overriding feature, selective fire, allowing the gun to continue firing until the magazine is empty, so long as the trigger remains depressed. Thus, a pistol or rifle must have this feature to be an “automatic weapon.” A sporting rifle is only sold to the pubic at large with a semi-auto firing mechanism, and no matter how much alike it appears to a military version, it still requires the trigger to be pulled, released, and pulled again for each and every round discharged. That is the definition of semi-automatic. Those of us who understand firearm’s know this, but this fact is lost on many non-firearms experienced pundits and firearms critics who see a rifle that is not a bolt or lever action design and assume it is an automatic weapon based solely upon its exterior appearance. And mind you, appearances can be deceiving, especially with modern semi-auto rifle designs.

The Sig Sauer Bravo4 was developed for use by the military, law enforcement and civilians as a premium optical sighting system for the MCX (shown in military combat configuration) and the MPX. (Photo courtesy Sig Sauer)

Still, even in the world of law enforcement (with few exceptions) fully automatic weapons are rarely deployed. Selective fire weapons are the purview of SRT (Special Response Teams) SWAT, and the military. When Sig Sauer introduced the MPX and MCX rifles a few years ago they developed military and law enforcement versions, as well as comparably styled civilian models that are only semi-automatic in operation. This very same distinction is still what separates a semi-auto AR-15 Sporter (or any AR platform-based semi-auto rifle used for hunting and sport shooting) from an M16 military rifle, and any other variation of the design used by law enforcement and military. In the world of air rifles, tactical and sporting models share this same distinction but are not limited by it. For Sig Sauer, however, they have adhered to this real world caveat by offering the CO2 powered versions of their MPX and MCX only as semi-auto models.

Mounted on the MCX airgun the Bravo4 is easily adjusted for windage and elevation to suit the range and velocity of the 4.5mm lead pellets. Although the Bravo4 sells for around $1,300 it is the one battle sight that can be used with any Sig Sauer rifle from a 4.5mm pellet model up to a .300 Blackout cartridge version of the MCX. In Part 3 we will also look at airgun quality optics for the MCX that are priced commensurately with the guns.

What is more noteworthy about the CO2 versions is the ability to equip them as one would the 5.56mm model, and we begin with the same optics available to both. While it makes little sense to put a $1,299 optic on a $220 air rifle, the fact that you can is what makes the Sig models viable training guns by utilizing the same accessories as the cartridge-firing models. Sig Sauer developed the Bravo4 as a superior sighting system for its tactical and sporting rifles by building it to withstand the harshest environment in the world, the battlefield. It offers an impressive 10 degree field of view which is 43 percent wider than traditional 7-degree optics. Put simply, the Bravo4 provides a 53 foot field of view at 100 yards, versus 37 feet, allowing an operator to see more of what’s surrounding the target. Able to fit any top rail, on any rifle, the learning experience with air quickly and affordably, (at least for the air rifle) enables a quick transition to live rounds. This only makes sense (and dollars and cents) if that is the end goal, but since the Bravo4 was on hand; mounting it on the MCX air rifle seemed like a great place to start shooting the Sig Sauer CO2 model.

Loading the magazines   

Externally, the CO2 Sig has the same lines and nearly same weight and balance as the 5.56mm model. The KeyMod-style handguard also allows mounting other accessories on the sides and bottom, but for this review only the vertical foregrip that comes with the CO2 model is being used. As noted in Part 1 the operating controls on Sig cartridge models are ambidextrous, on the CO2 models this only applies to the safety and charging handle, and magazine release on the right side of the mag well. The magazine itself is one of the airgun’s most outstanding features as it allows 30 pellets to be loaded per magazine.

The genius of the MCX and MPX airgun design is in the magazines which use a 30-round rotary pellet belt. The belt is accessed through a loading port in the side of the magazine. It is shown here in the first position (paired black pellet loops aligned in the center) to begin the loading process. Lift the first loop of the second pair and pull it upward. 

Belt fed pellet magazines are not entirely new, the Umarex Beretta CX4 Storm tactical air rifle uses one, (as will the forthcoming Sig Sauer P320 CO2 pistols), but Sig Sauer’s approach for the MPX and MCX is certainly innovative. If you can picture a belt fed machine gun, you know that the cartridges are inserted onto a belt that feeds the ammo into the action. It’s the same basic principle behind the Sig’s magazine only it is a closed loop design. Opening the side panel on the magazine exposes the pellet belt, which has to move only in a clockwise direction. If you hold the magazine upright with the loading panel raised, always work in an upward direction, as moving the belt counter clockwise (or downward) will damage the internal components. The belt first has to be removed from the magazine which is done by finding the end of the belt (the only portion that does not have white and silver pellet chambers), lifting it off the feeding track and pulling it slowly upward and out of the magazine.

The magazine design uses a plastic and metal chain linked belt that pulls up and out of the magazine to load. Always work in an upward or clockwise direction starting from the right side (as shown) when removing the belt.

Once the belt is removed, it is laid flat with the metal retainers facing down and pellets inserted nose first (as seen in the first 10 pellet loops) and securely pressed flat against the loop.

The belt is then laid on a flat surface with the silver portion of the pellet loops facing down. Insert a 4.5mm pellet nose first into each loop on the belt making sure the skirt is flush with the back. Once all 30 have been loaded, the belt is fed back into the magazine (once again going clockwise) until the end of the belt is back in the channel.

All 30 pellet loops, including the four all black loops, are loaded and then the belt is reinserted into the magazine from the left (as shown) pushing it clockwise into the magazine’s channel.

Close the loading port cover, and the magazine is ready to be loaded into the MCX. If that sounds like a bit of work it is, but spare magazines come with three belts, so you can have two pre-loaded in reserve to quickly interchange, as well as extra loaded magazines. It is a remarkably efficient design and the same standard capacity as a .223 (5.56 NATO) AR-15 magazine.

When the entire belt is properly inserted the black loops will be centered in the opening and the entire belt secured in the channel. Close the loading port and the magazine is ready to load into the MCX. Spare magazines come with three extra pellet belts which can be pre-loaded.

Loading the 88 (or 90 gram) gram CO2 into the MCX is a very quick process by squeezing the release on the right front of the shoulder stock, removing it from the receiver, threading the 88 gram CO2 canister nozzle into the rifle, and replacing the shoulder stock over it.

The CO2 system for the MCX uses an 88 gram cylinder that is easily threaded in to the back of the receiver by removing the shoulder stock. The large locking release (at right) is simply depressed and the stock slides out.

The CO2 cylinder threads directly into the receiver and is shrouded by the shoulder stock when it is replaced. Very quick and easy to do with no tools required.

Now that we’re loaded it’s time to sight in the Bravo4 and see what this Sig Sauer air rifle can do.

Locked and loaded, the Sig Sauer MCX CO2 model with the Bravo4 optics is ready for the firing line. For a long shooting session, a tactical vest like this model from UTG will hold extra pre-loaded magazines, as well as a Sig Sauer P226 air pistol and spare mags.

In Part 3 we head to the shooting range, look at less expensive air rifle optics and test fire the MCX.

5 thoughts on “Sig Sauer MCX Part 2

  1. Like you , I believe that most of the controls could have and should have been made operational, not inert. That cheapens the airgun, period. I disagree with the SIG attitude that it is semiauto because that is what is available to civilians. Here is a wake up call to SIG. Air gunners buy these to have some fun with select fire, because for the most part civilians can’t obtain select fire firearms. If there was no market for select fire airguns they wouldn’t be offering the UZI and the new MP40. A pretty poor excuse. If you think by not offering select fire ,anti anything that shoots anti gunners will be on your side , don’t forget to put that tooth under your pillow tonight.


  2. I do not believe Sig Sauer had any intent in making the MCX and MPX airguns semi-auto only other than for efficiency of production, as it requires a more complex firing mechanism for selective fire and thus increases the retail price. The same can be said for a number of AR-style CO2 models which follow this same course. I can see where the demands of consumers could influence future designs by Sig and others to offer selective fire versions of models that have that feature, like the current Mini Uzi, Mauser M712, and forthcoming MP4, not to mention the recent Umarex Beretta M92 A1 which is a selective fire model (and an excellent one) even though that version of the Beretta 92-Series (93R) is long gone from Beretta production. If any selective fire pistol design should be resurrected in .177 caliber that would be it. It is available as an Airsoft pistol, which is an interesting choice.


  3. Although the Beretta CX4 pellet magazine is not an exact replica of a CX4 cartridge magazine, I think I like the CX4 pellet magazine design more than the MCX / MPX pellet magazine design. The CX4 pellet belt is a permanently mounted part of the magazine with open sides that make all of the pellet holders readily accessible for loading.

    Has Sig Sauer said anything yet about the CO2 loading mechanism in the new P320? Is it the same cam mechanism used in the P226?


  4. You are right that the Beretta rotary magazine is much faster to load initially, but it is also far more delicate and easily damaged, and the real advantage with the Sig design is the speed with which pre-loaded pellet belts can be inserted into the magazine shell. I have compared both, they both work well, but the Sig has some solid advantages in speed and durability.

    I have not yet had a chance to get my hands on the new Sig P320 but I believe the CO2 design will be similar while the magazine is a totally new concept for a pellet-firing pistol, and based on the MCX and MPX designs.



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