Sig Sauer MCX Virtus: A Carbine Built for Serious Work

People were impressed when Sig Sauer introduced the original MCX. The new MCX Virtus is an improved version of a serious gun designed for serious work.

Sig Sauer MCX Virtus: A Carbine Built for Serious Work

If you have customers who really know tactical equipment – equipment built for serious work such as enforcing law, fighting wars or defending the household against intruders — you are likely already carrying Sig Sauer firearms. And a version of the MCX called the Virtus is going to get those customers’ attention. It’s not a hobby gun built for the occasional weekend shooter, but for real world conflict where equipment is stressed and must still work. It’s used by some special forces units.

People were impressed with the original MCX when Sig introduced it a few years ago. With controls in the same place as the AR-15, transitioning from the AR is easy, but the different operating system Sig designed makes it a better weapon system.

Among the differences is the short stroke piston system that replaces the original AR’s direct gas impingement system. The argument continues as to which type of system is better, but many choose the piston system because it does not deposit hot gas and carbon directly into the bolt and action. The gun runs cooler and cleaner, improving service life and reliability.

The piston system isn’t the only difference. Dual recoil springs ride above the bolt and its carrier doing away with the receiver extension tube allowing the buttstock to fold for stowage and transport. The buttstock is also adjustable for length and comb height and in an emergency, the gun can be fired with the stock folded.

Additionally, you can quickly change barrels in the field. Sig offers barrels in either 5.56 NATO or .300 Blackout in various lengths, so in combination with different buttstocks, colors and handguards, the MCX Virtus has more than 500 configurations. It’s one of the most versatile small arms available anywhere. And once your customer buys an MCX Virtus, you have the opportunity to sell conversion parts. Many parts that are compatible with a basic AR-style firearm work with the MCX, including pistol grips, magazines, muzzle devices, optics, iron sights or anything that can be attached to an M1913 rail or an M-LOK compatible handguard.

Barrel changes require only a Torx bit to loosen two bolts that are revealed when the handguard is removed. Then the barrel assembly is pulled straight forward away from the upper receiver and the replacement barrel inserted. The bolts are then tightened and a handguard of the selected length is installed.

First Impressions

I received two carbines for evaluation. They were identical Virtus units except one was finished in Flat Dark Earth and the other in what Sig calls Elite Concrete, which is a pleasing medium grey color. This provided a fairly unusual opportunity to compare two identical guns to see if manufacturing specifications and standards were consistent.

Trigger pull on both guns was nearly identical with some take-up — the Matchlite Duo triggers are two stage triggers — followed by a little creep and then ending in a surprise break. There are better triggers on the market for match work, but these triggers are installed on duty guns, so a very light trigger is not appropriate. Break weight for both was a little less than 5 pounds with mere ounces of difference.

Each gun was supplied with a Lancer 30 round L5 Advanced Warfighter smoke-colored polymer magazine sporting steel feed lips that are designed to last. When full, both magazines were a little difficult to fully seat on a closed bolt, but other AR-15 magazines were not. There were a few failures to feed from GI-style magazines early in my shooting, but after a short break-in period, all the difficulties went away.

Accuracy was exceptional for a patrol or duty carbine. Both guns, when scoped, regularly printed groups averaging between one and two inches from a bench at 100 yards, and both delivered some sub-minute of angle groups proving they are capable of good accuracy for the right shooter with the right ammunition.

Special Features

The MCX Virtus has many features that make the gun user friendly. Besides the folding buttstock with five positions for length of pull and ability to be moved up or down to adjust comb height, the hollow pistol grip has a plug that is securely held in place but can be removed so small items can be stored. 

The trigger guard is bowed so there’s plenty of room for a gloved finger to contact the trigger, and the magazine well is nicely beveled to encourage quick magazine changes. The magazine release button is ambidextrous, as is the safety. And unlike the AR-15, the safety can be engaged when the gun is not cocked. The bolt catch is not ambidextrous, but does have an extension at the bottom, making it easier to depress than a standard AR catch. The MCX charging handle is also ambidextrous, but is not interchangeable with standard AR-15 charging handles.

Sig installed a bolt forward assist in the same place as the one found on a standard AR-15. Using a forward assist can cause more severe problems than a round that won’t chamber. It can force a round so tightly in the chamber that the gun simply stops working, so savvy operators will push the bolt itself forward with finger pressure on the right side of the bolt or simply recycle the charging handle to fully seat a round. 

Optics, Ammo

The MCX Virtus does not come with iron sights — creating an oppurtunity for accessory sales for dealers. The top of the gun has an M1913 rail running from the rear of the upper receiver to the front of the handguard allowing plenty of room for the installation of iron sights or optics.

Sig supplied one of its Romeo 4T compact red dot sights for use with this review. It runs on battery power from a CR2032 coin battery and by solar power. The reticle is either a two minute of angle (MOA) dot or the same dot in a 65 MOA circle. The center dot can also be set up with three dots below it that can be used as bullet drop compensators, so there are actually four reticles included that can be selected by simultaneously pressing two buttons and toggling through the options. The 4T has 10 daylight settings and two night vision settings, can be mounted for co-witnessing with iron sights, shuts off automatically after two minutes of stillness, then turns back on to the last setting the moment the sight is moved.

Sig also supplied some Sig Elite Performance Match Grade Open Tip Match ammunition. It proved to be accurate in combination with both sample guns, again confirming consistency in manufacturing quality.

The 16-inch cold hammer forged steel barrel has a 1:7-inch inch twist for the 5.56 NATO chamber and a screw-on, three-prong flash suppressor. The gas block and valve have two positions and the valve is easily adjustable through a window in the handguard so that the handguard does not have to be removed to change the setting. One setting allows a bit more gas to be delivered to the system, but for normal unsuppressed operation using 5.56mm ammunition, the valve is set to the lowest setting. If function becomes sluggish and there is no time to stop and clean the gun, the more powerful setting can be selected.

Sig collected recommendations from the special operations community and sent over one million rounds down range testing the MCX Virtus before it went into production. The company says that each gun will fire 20,000 rounds before any part needs replacement, which is a lot more than an AR-15 is built to shoot before parts need to be changed. 

With an MSRP of $2,233 for the Patrol model shown here, it’s much more expensive than the typical AR-15 hobby gun. But then again, this is a serious gun for serious work. 


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