SIG Sauer MCX VIRTUS Long-term Endurance Test: Part 1

EDITOR’S Note: When we first ran this story the SIG Virtus was still difficult to find on dealer’s shelves. As one of the most reliable semi-autos we’ve ever seen tested, it’s worth looking at again if you are in the market for enhanced reliability. There’s a reason that the SIG Virtus is the weapon of choice for many of the military’s “special teams.”

Last month, I was handed the new SIG Sauer Virtus rifle for review, my first test item in the MCX family. Though initially, I was skeptical, the Virtus turned out to be very impressive weapon system. It uses a unique operating system, an entirely new piston driven action developed in-house by SIG Sauer.

Long-Lasting Endurance?

Between that and the user barrel change capability, this is a great leap forward in rifle technology. Still, questions remained. As a retired soldier, some habits die hard. I always look at new and wonder about the durability. The first thing my unit always did with something new was going beat the living shit out of it, to ensure it wasn’t going to quit at some critical time. When you roll around Indian Country in a six- or 12-man team for a living, you have to know your equipment works.

Like many of you, I lived through the “piston revolution” of the early 2000s. The “new” idea of a piston in place of a gas tube was going to take the AR-15/M16 family into the future. We all know how well that worked out. Piston systems tended to be heavy, recoil like a train wreck, and introduced new problems in place of old ones. Also an issue, they tended to lack the accuracy of direct impingement rifles, a deal killer when normal AR’s were rapidly approaching a 1 MOA standard. Pistons slowly began to die off. The alleged reliability gain was small potatoes since it turns out normal AR-15’s are incredibly reliable in the modern era anyway.

Check out the initial review of the SIG Sauer Virtus.


The SIG, out of the box, proved to be a different animal. The recoil is extremely mild on this platform, it isn’t front heavy, and accuracy is as good as anything. I started this week’s video with groups around 1 MOA, which then shrank to ¾ MOA, and finally turned in two separate ½ MOA 100m groups. We can reasonably assume I got warmer on shooting, the gun was capable all along. Those are impressive numbers, ½ MOA being the best I can do with anything on most days.

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No Parts Replacement for 20,000 Rounds?

My big question with this weapon is the durability. SIG says it shouldn’t need any parts replacement for 20,000 rounds, which is amazing. They also contend the piston system is extremely reliable and will outperform any direct impingement (DI) rifle. Now 20,000 rounds would require a huge investment of ammo and time to test. But we do want to know. So we devised a test to short circuit that number.

I’ve taught a lot of CQB in the U.S. Army, so I know a way to get a DI gun so dirty in short order that it will stop functioning. Suppressors filthy a gun up like you wouldn’t believe if you don’t own one. In my experience, even rattle trap government guns will stop working correctly around 500 rounds of suppressed fire. So I proposed to SIG that we should run a test on the VIRTUS, 2,000 rounds suppressed without a cleaning. In typical SIG fashion, not only did they cowboy up, they provided the ammo.

Going quiet — Why It’s Smart to Purchase a Can.

If the VIRTUS continues to run flawlessly, it will be incredible. And the boys at SIG seem to think it will. That is a huge milestone. But I do want to know exactly how much punishment we can dish out, and the test if successful will be of massive benefit to the normal consumer. If I can go 2,000 rounds suppressed without a cleaning, you should be able to go 10,000 un-suppressed. Clean your rifle once a year, whether it needs it or not.

Initial Ruminations

Predictions wise, I think we might have to take the suppressor off and knock the carbon out of it every 600 to 800 rounds. That is not a functional issue, it’s an accuracy one. In my experience in the military, carbon build-up starts to really play hell with group size around that time.

The SIG MCX Virtus is configurable in 500 different combinations. Pictured above is the SIG MCX Virtus Patrol in 5.56.


This also allows us to really wring out the SIG SRD556. SIG has been batting them out of the park in suppressor technology this year, and we have the SRD556 in-house.

During accuracy testing this week, the first thing I wanted to know was suppressor shift and was it repeatable. SIG uses a taper lock system on their barrels, which is supposed to increase repeatability. Initial tests say this is correct. In five cycles of taking the suppressor off and reinstalling, my shift was exactly the same each time. The SRD556 also proved hearing safe even with supersonic ammunition. Shooting the first 300 rounds of this test without earplugs was a nice change!

Lasting Impressions

We have many rounds left to send down range,  enough that this test will be at least a three-part series. I have a bunch of challenges lined up for this rifle over the next month. It is winter, so we can add extreme heating and cooling cycles to that list for good measure. If you have a test you are curious about, add it to the comments section. And we will be back in a few weeks with Part Two.

For more information about the SIG Sauer Virtus, click here.

To purchase a SIG Sauer Virtus on GunsAmerica, click here.

About the author: Clay Martin is a former Marine and Green Beret, retiring out of 3rd Special Forces Group. He is a multi-decade and -service sniper, as well as 3-Gun competitor and Master ranked shooter in USPSA Production. In addition to writing about guns, he is the author of “Last Son of The War God,” a novel about shooting people that deserve it. You can also follow him on twitter, @offthe_res or his website,

{ 9 comments… add one }
  • William Bainbridge March 25, 2020, 7:07 am

    If you really want to dirty up the Sig and check for stoppage you might not only want to blow through the Sig ammo but maybe some steel cased Tula and or Wolf.

  • michael Hughes March 23, 2020, 6:55 am

    In the video, clay says that piston guns run dirtier than DI guns. I thought it was just the opposite

  • Jon January 22, 2018, 1:13 pm

    True test comparability requires that the Sig rifles be tested using the same build and technology level of the suppressors being used in actual military service. Why? The test premise is based on the carbon build up the military suppressors produce whereas, Sig suppressors are calibrated to produce the same level of “gumming up” and therefore will produce false comparison “dirt” readings.
    The same issue applies to the ammo. Have Sig “generously” provide standard military spec ammo that is used with those mil-spec suppressors.

    If you do not adhere to comparable standards, then this becomes a silly exercise and is ultimately boils down to another biased “freebie” marketing/PR job for Sig.

  • E. Sheahan January 9, 2018, 6:08 pm

    Great job asking and answering whether the zero would hold after taking off and putting back on the barrel. I would be really interested in seeing the point of impact shift between the 5.56 and the .300 Blackout. I, unfortunately, bought the MCX thinking that it would be Sig’s answer to the AR platform progression. Disappointment with Sig aside, for the total abandonment of the MCX for the new Virtus, non-compatible, non-retroactive, thanks for the VERY expensive-to-you, free to us, Beta test, screw over, I am currently waiting for a 5.56 16” barrel to compliment my 11.5” 300. Do you plan on using two scope, with separate mounts, when shifting from one barrel to the next? Or, are you planning to track the POA/POI shift and dial accordingly? Lastly, thanks for sharing the suppressed round-count-cleaning advice. I am tracking a round count without a suppressor on a Bushmaster and am running well after a year of non-cleaning. I did not realize the impact of shooting suppressed would have (I always breakdown and clean my MCX when I return from range).

  • John Escalante January 8, 2018, 9:41 pm

    I have a CZ455 American combo 22LR 17HMR AND I want to get a suppressor for it. Is it cheaper to send both barrels in to get threaded for a suppressor or buy both already threaded for a suppressor

  • Jake January 8, 2018, 11:33 am

    How do you think this beast will be for upgrades or changing stocks, hand guards etc? I put a Magpul PRS on a SIG M400 Hunter 20″ for my son-in-law. Instead of five minutes it took at least an hour. SIG used Red Loctite on the A2 stock screw! Please report if you find any surprises like that.

    • PA G January 8, 2018, 12:02 pm

      The compatibility with AR parts is limited. The only thing I was able to swap on mine was the safety (it will accept a standard AR one). The stock, trigger and charging handle are proprietary and interchangeable only with other MCX-specific accessories (like the Geissele trigger and charging handle – I can confirm those work on the Virtus). The handguard is also proprietary since it’s a functional part of the piston system.

  • Merrill Rick January 8, 2018, 6:13 am

    Something Colt, 1911, Defender, 6920 Ar15 thanks.

  • Mahatma Muhjesbude January 8, 2018, 6:00 am

    Hey Clay! That Lizard Camo is AWESOME! If that Alien Predator was wearing it Arnold would never have been able to take him out!

    As for this Sig AR, if it’s as ‘durable/reliable’ as they expect and your tests prove that out, and you think it can handle sustained full auto firing without overheating, Sig should immediately offer the military this as a lighter weight compact CQB SAW Belt FED version with about a 300 round capacity in the bag?

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