Gun Review: SIG SAUER MCX Rifle
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Sig Sauer developed the MCX rifle for America’s special forces. Their goal: a lightweight firearm that’s as quiet as an MP5, as deadly as an AK-47, and more modular than anything ever designed. Originally chambered in 300 AAC Blackout, SIG built the MCX rifle to fill the same need that inspired AAC’s Honey Badger.

I’ve been watching the SIG SAUER MCX come together for well over two years, from the first prototypes to the finished product. The military and law enforcement version is a useful firearm; even with a massive silencer attached, shooting in full-auto, the SIG MCX is extremely controllable. It’s more like a big MP5 than anything else.

My biggest concern: would SIG translate the mil spec masterpiece into a useful civilian semi-auto rifle? They certainly started on the right foot . . .

Gun Review: SIG SAUER MCX Rifle

The rifle sports a pencil profile (a.k.a., superlight) barrel (this version in 5.56 NATO). The weight savings is significant; unloaded, it tips the sales at a scant six pounds. The gun also has excellent balance, which makes it incredibly easy to maneuver. When it comes to getting shots on multiple targets quickly – especially when shooting with a silencer attached – an MCX-wielding rifleman will have a distinct advantage.

The muzzle is threaded in SIG Sauer’s nifty taper design (drawings available here). It gives their silencers a better grip on the muzzle, helping the can stay tight on the rifle – rather than walking off and getting into trouble (ballistically speaking). A silencer that doesn’t stay put will have an enormous impact on a firearm’s accuracy. If you don’t have a SIG Sauer silencer or compatible device, no worries — the design works with all existing 90 degree shoulder mounting devices.

Gun Review: SIG SAUER MCX Rifle

The hand guard is a lightweight skeletonized keymod affair. The guards extend about 12 inches on the barrel for a good length of pull. For those who want the proper MCX experience they’re roomy enough to slide a silencer underneath. Those seeking quick barrel changes or access to the gas system for maintenance will be pleased to discover that the guards detach more quickly than a lectured teenager. Pull out the front takedown pin and slide the guards off the front of the gun — done. The set-up also means they can be a tiny bit wobbly, but the integrated Picatinny rail on the upper receiver’ s top extends out to the gas block to provide a solid mounting platform for optics.

Barrel changes are easier than coming-up with a metaphor for something easy. With the hand guard removed, you lock the bolt to the rear and unscrew two hex screws on the side of the chamber. Once unscrewed the barrel slides right out. I don’t know of a more effortless design. It’s well made too — like the rest of the gun. The MCX’s fit and finish is superb. Unlike the MPX, for example, the MCX’s upper and lower receiver are precisely mated. Every line matches up on both parts. It’s a thing of beauty.

Gun Review: SIG SAUER MCX Rifle

While the SIG MCX kinda looks like a standard AR-15, there’s one major difference: it’s gas piston operated. Buffer and gas tube? Gone. SIG’s replaced them with a short stroke gas piston and a compact recoil system contained completely within the upper receiver. To provide the force necessary to stop the bolt carrier’s rearward movement and return it to battery after each round, the MCX features a pair of recoil springs directly attached to the bolt carrier. Because the recoil springs are housed where an AR-15’s charging handle would normally sit the charging handle has been moved slightly higher than normal on the receiver.

When you run a suppressed rifle the added back pressure from the silencer creates additional force to the bolt carrier, which makes the rifle cycle faster. That’s not good; it can become uncontrollable and cause excessive wear on the operating bits. The MCX has an adjustable gas system that changes the amount of gas being sent to the piston, controlling the cycle rate. The system’s equipped with a gas regulator that the shooter can adjust on the fly.

[NB: There are currently two MCX version on the market. The first (sold through Cabela’s) uses a self-regulating gas system that vents super-heated gas directly into the air to control the pressure. The latest and now official version uses a closed system manually adjusted from “suppressed” to “unsuppressed.” The official word from SIG Sauer: the adjustable gas system was done on request, but they settled on the manual system to make the civilian MCX be as close as possible to the military MCX.]

The MCX’s relocated charging handle adds a bit more material to the top of the receiver. It isn’t much and it doesn’t throw off the gun’s ergonomics, but it’s a bit of a step backwards, svelteness-wise. That said, the upper receiver’s added bulk meant that SIG could do away with almost the entire back half of the rifle.

Gun Review: SIG SAUER MCX Rifle

As the MCX’s recoil system is completely contained within the upper receiver there’s no need for a buffer tube assembly. So SIG Sauer sliced it off the gun. Instead of the usual screw-in stock adapter, SIG crafted a completely new rear for the MCX: a vertical Picatinny rail to attach their skeletonized stock to the gun. It’s a brilliant move given that the rail’s design is already in public use; aftermarket parts will be simple to produce and even easier to configure. (Rock River Arms has a similar system on some of their piston powered rifles. They claim it isn’t actually a Picatinny rail but a proprietary system and refuse to sell a stock to anyone without first seeing a copy of an approved Form 1.)

The MCX’s standard stock features a knuckle, allowing the stock to fold flat against the side of the rifle. A folding stock is generally better suited to short-barreled rifles, but anyone who likes to cram a bunch of rifles into a gun case will be thankful. There’s also a QD cup built-in for sling attachments and such.

It looks like the ergonomics of that folding stock would be about the same as the ergonomics of a piece of rebar, but in reality the gun still feels pretty good. I was able to get a proper cheek weld on the gun with no problem and the way that the comb of the stock is designed felt like a slightly slimmer version of a standard AR-15 stock. No complaints from me there.

Gun Review: SIG SAUER MCX Rifle

The SIG Sauer MCX’s fire controls are ambidextrous. Mostly. The safety selector — available on both sides of the gun — was specifically designed not to impede precision shooting or dig into the shooter’s finger. The rifle’s handsome extended magazine release button is ambi as well, enabling efficient left-handed mag changes. The charging handle also goes both ways too (so to speak), with latches on both sides of the receiver. Unlike the Sig MPX, the MCX’s bolt release is only available on one side of the gun. It isn’t a deal breaker but it’s a design feature I really liked on the MPX.

There’s a QD cup built into the rear of the lower receiver on both sides, but it’s more than “just” a set of QD cups. SIG joined the two cups with a hole through the center, which allows for a whole host of new sling and retention options. Another improvement: instead of the usual post-production bolt-on trigger guard, the MCX’s glove-friendly trigger guard is molded into the receiver. Nice touch.

The trigger is a whole lot less than wonderful (i.e. awful). It’s heavier than a sumo wrestler carrying a small Toyota. Creepier than finding a sad clown doll in the back of your car. It stacks more than the set design for Future War. I’ve said it before (which not-so-coincidentally rhymes with Tavor): an awful trigger can ruin a good gun. Accuracy is finite. When you can’t get a proper trigger pull, it’s impossible to achieve a rifle’s maximum accuracy.

Gun Review: SIG SAUER MCX Rifle

When I first picked up the SIG MCX, I was deeply enamored of the prototype’s look and feel. The production model still feels solid and well-built as those first prototypes and svelte to boot. As I mentioned above, the pencil thin barrel balances out the lightweight skeletonized stock, keeping the gun from feeling front heavy. That makes the gun a pleasure to maneuver around the range.

Gun Review: SIG SAUER MCX Rifle

I mounted iron sights and a red dot, then slammed hundreds of rounds through the barrel using everything from massively expensive Federal Gold Medal Match all the way down to reloads I picked up at the local gun range for a few pennies a round. All of the factory ammunition ran just fine. In two cases, the reloads failed to completely chamber — I think you can figure out why (pictured above).

Two more rounds from the same lot with similar deformities failed to chamber in my PWS rifle as well (whose reliability I haven’t had a single reason to question after a few thousand rounds) so I’m chalking it up to crappy ammunition. Still, I’d run factory new ammo if I needed the gun be 100 percent reliable. Just in case. Then again, advising people to run factory ammunition and not crappy reloads is probably as close to “common sense gun safety” as you can get.

Gun Review: SIG SAUER MCX Rifle

I tested the rifle’s accuracy at 100 yards using Eagle Eye Ammunition .223 Remington ammo. Eagle Eye ammo is our official ammo sponsor for accuracy testing for one simple reason: it’s the most consistent ammunition I have ever tested. Feeding our guns Eagle Eye allows us to directly compare the accuracy of multiple firearms. Just like my other accuracy tests, I configured the MCX with a bipod and rear sandbag. Just like you would shoot it real life — no lead sleds here! Here are the results.

Gun Review: SIG SAUER MCX Rifle shooting target

This was the best five round group of the day. Ignoring that flier for the moment, even with a crappy less-than-ideal trigger the MCX is capable of shooting well under 1 MoA. In fact, it’s sitting right around 3/4 MoA. That’s twice as tight as Beretta can manage with their latest “precision” rifle, all from a pencil thin barrel with a crappy challenging trigger, shooting off a sandbag. Some better glass and a better trigger would bring that group into the 1/2 MoA range. But there’s a problem I may have mentioned before. Dear SIG Sauer: this is what happens when you ship an awesome gun with a crappy inadequate trigger.

Gun Review: SIG SAUER MCX Rifle Shooting Target

That flier, 100 percent shooter error, brings the group out to 1.3 MoA. Still better than Beretta and well within the realm of “acceptable,” but the first four rounds prove that the gun is capable of greater accuracy.

Gun Review: SIG SAUER MCX Rifle

The MCX looks great, the concept behind the operating bits is fantastic and the execution is spot on. While its accuracy is on a par with rifles in the same price range, it exceeds its competitors’ functionality and modularity.

Can you swap the stock on your AR-15 in 30 seconds – with just an allen wrench? Remove the hand guards in 10 seconds flat? Got an adjustable gas system for your suppressor? Nope. Even without a Giselle-class go-pedal, this rifle is well worth the price of admission. Add that little after market touch-up and it’ll be head and shoulders above the rest.

Specifications SIG SAUER MCX Rifle:

Caliber: 5.56 NATO
Action: Semi-auto gas piston
Barrel Length: 16″
Weight: 6 pounds
MSRP: around $2,000 via Brownells

Ratings (out of five stars):

Accuracy: * * * *
The gun is mechanically capable of much more accurate groups. A $200 trigger upgrade would add that extra star.

Ergonomics: * * * * *
I love it. It fits me perfectly, balances well and feels right in my hands.

Reliability: * * * * 1/2
So long as you feed it factory ammunition you’ll be fine. As always, reloads can cause malfunctions. Just FYI.

Customization: * * * * *
From changing out the barrel to swapping the hand guards, the ability to customize this gun is amazing in both simplicity and scope.

Overall: * * * *
Trigger-denied perfection.

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    • MSRP: $1,866

      I knew I made the right decision NOT buying one.

      Sorry for raining on your parade. I hope you really enjoy your new rifle … It is a pretty cool toy. Personally, I cannot justify that much of a cash outlay.

        • I picked up an MCX with 5.56 barrel for $1,429.00 new at Smoky Mountain Knife Works in Sevierville, TN on black Friday. Nice rifle, very accurate if you change the trigger out.

          • Mike,

            Does the MCX come with two barrels as some owners said on blogs (5.56 and 300 AAC)? Congrats!

            I’ve been looking at bulk ammo purchases and 7.62 Russian is the cheapest. .223 or 5.56 is next then 300 BLK is scarce and the most expensive.


            • Rick, my understanding is that there is a sku for the two barrel (.300/5.56) version but I’ve not
              seen the actual sku quoted anywhere. Sig CS may be able to clarify that. Mine is arriving today and
              the sku is RMCX-300B-16B-TFSAL-P which is the .300 Blk model with no additional barrel.

            • forgot to add, I’ve also got the Folding & Telescoping 1913 interface stock on backorder and the sku is

              • Thanks Dave. Good luck with the rifle, it’s a good one. My dealer near me cannot get one in 300 BLK but i’ve found one on the web – ready to go. 300AAC is a great round but it’s so hard to find for less than .80c per rnd and in bulk of more than 500. SIG is awesome.


        • I purchased my MCX from a local dealer for around $1600. It came with 5.56 barrel setup only. I have had a 300 BLK before and hope to get the 300 conversion someday when it becomes available. Gun guys have all kinds of opinions on the 300 BLK. I think the only real advantage over 5.56 is to shoot heavy subsonic bullets from an SBR suppressed. That is the direction I will take my MCX. 300 BLK ammo is more expensive, unless you reload. I do. I have 2000 + bulk LC cases. 30 cal bullets are easy to come by, powder and primer are all now readily available too. I would not want to have to buy factory ammo for it.

          • Hoping that the 556 barrels come down in due time from the current $750. If anyone knows of someone wanting to sell or trade their Sig MCX 556 barrel, please advise. Tks.

      • Typical sig. Make a really nice firearm and put a crappy trigger on it. I have a great 226 with a fantastic trigger and love it. My son was so impressed he bought a 45 cal handgun from them. Lousy trigger and he called Sig and they said they could make it a nice trigger for $150 plus shipping both ways. Not worth paying high $ and halving to put a new trigger on it.

      • Hey guys The Ar15 MCX my husband is in the Military was Special Forces Seal he only buys the best so your all definitely in the gat. I have a? I’m trying to buy him due to him using his sig mcx special fully auto 3 sights 4 lasers , it’s one of a kind well all his team guys right now all carry exactly the same

        I if anyone can please help me I am looking for aftermarket products like to change his black to it’s like a desert camo also he locks his stock so it ,he never folds it since he’s shooting it more he was discussing changing the stock to a closed more or less look more like his assigned weapon like the M4 , does anyone know how or where I can buy him the camo I guess from seeing a YouTube video pretty easy it’s a package seen them very cheap prices also the Stock is important with nice padding , he’s now on the borders where an why he cannot tell me so I’d like to get him these gifts I’m sure that you guys know everything where I can buy hopefully . Please if anyone can help please Contact me@

        • If anyone would like to see it please let me know of course he has one of 4 lasers one is of course the best it’s where I work at Linq …. Again for helping me out to give my best friend and my husband a gift just because he’s so busy I will definitely take care of some one with a laser sight

      • I buy AR parts for often less than $600 per gun. I have run three calibers (5.56, 7.62×39 and 300 BO) I prefer the 7.62x39ers. Three of them for one of these is a tough choice (folding stock). Nah, . .

    • Im with you. I wish I could buy one now (can’t afford it) but if I could i would snatch it up in a second. It fixes so many problems that we shooters have. Don’t like the caliber? Change it to .300blk. Cant find .300blk? Change it back to .223. Run it suppressed? Change the gas setting. It is the logical conclusion to the AR style platform fixing many of its short comings and doing so at a competitive price point. Like Nick said, with a trigger upgrade you are looking at a sub 1 MOA rifle for less money that most high end ARs, with twice the modularity of any AR. This is a no brainer.

      • That’s an interesting point. I have yet to see a “high end” AR-15 push the $2k mark. (Which is what you’re looking at for this thing with a decent trigger.) It goes back to the question of what does this thing do that a SCAR 16S doesn’t?

        • As for price point; check KAC, LWRC, LMT regularly push that boundary, add the myriad cluster that is the botique ARs, and you know why he would say that. This is lighter than a SCAR 16, still less expensive, more modular, was built from the ground up to be suppressed, compatible triggers with current ARs, you can use AR Lowers with this upper, barrels and furniture are more modular and easier to interchange, It’s also not as fat, and I’m not stuck with a short cheese grater handguard (with Uber expensive and heavy additions). I’d say it’s lighter. Oh, and this already has 1 caliber conversion, more are coming.

        • What this does that a SCAR16s doesn’t do? The SCAR isn’t that great of a gun. The Rangers dumped theirs quick to go back to the M4 for a reason.

        • Old post, but the MCX is in the news. As others have said, there are plenty of high end AR’s out there that push 2,000$ out of the factor with far less features than this rifle. Are they great rifles? Darn right and I would be happy to own one. What I am saying however is that the MCX does more in terms of modularity, innovation, and bang for your buck at competitive prices. You aren’t shelling out 1,800$ for an AR clone, it is built to be more efficient, shorter, and run better with suppressors with the capability of easy caliber conversion. If none of that matters for you, absolutely choose another gun but for those that plan on using those features, this is a no brainer as I have said. It is going to be far more reliable and less gassy with a suppressor, it has a shorter length of pull than a standard AR and a SCAR while being just as light as an AR and less than a SCAR. All this for a street price of 1,500$ currently. So yes, it is a success and as long as the market supports the rifle in terms of parts and customer service. As a stand alone design? SIG did take the standard AR game and added plenty of features in a market where people happily pay 1,500 to 2,000$ for an AR from the factory with nothing more than a brand name and some marketing verbage like the LVOA (low visibility operational something or the other”

  1. Nice review, but one Q: you say gas operation is a _difference_ from the AR-15? Is gas impingement not ‘gas operated’?

    • It is a gas piston design like an AK or other piston driven AR platforms like Primary Weapon Systems MK1 Mod 1.

  2. Good review, interesting gun. I want one badly. That being said, I refuse to be a beta tester for sig a second time (556xi). Once the first few thousand have been wrung out for a year or so I may jump in the bandwagon. Nick, how was accuracy once it got heated up a little bit. The pencil barrel has me wondering.

    • I was a beta test for the 556xi as well as the first gen MPX both promising caliber exchange kits in the early days only to fall short. With the MCX I made sure I had the correct SKU for the 300 BLK/556 barrel combination. I also made sure there wasn’t any confusion and the gas system was the final manual version and not self adjusting. The complete set up came in a black plastic “MCX” logo’d case instead of the typical cardboard box & stores the additional 556 barrel nicely in a foam cut out. Not a heavy duty traveling case w/metal latches, but still nice enough to go back n forth to the range. Final price on the 300/556 SKU was $1,799. Absolutely love this rifle!! The weight difference between the 556xi and MCX was more noticeable than I imagined. The MCX is VERY comfortable and has great balance. I thought I’d keep the 556xi but after just one afternoon the xi is “for sale.” Swapping out barrels between 300 & 556 is almost too simple; making me think I was forgetting something. After 2 disappointments (556xi & MPX) SIG got the MCX right. As far as the trigger, I’m ok with it and don’t plan on changing it. It would be hard to make significant improvements to such a great rifle but I wouldn’t be surprised if SIG applied it’s LEGION marketing tactics to the MCX; offering an improved trigger, options on the stock & sights, logo’s, addl mags and a special case so they can justify increasing the price. It worked on the 226 so I’m sure a rifle is next and the most logical candidate seems like it would be the MCX. “The MCX LEGION…..hmmmmm”

  3. Honestly, at that price point I would expect at least a decent trigger. That’s disappointing. The decision not to produce an M-LOK version of the hand guard really kills it for me. (All my latest rifles are M-LOK based because of the weight savings and improved air circulation inherent in the system.)

    Yes, people will bug me about counting ounces on an eight pound rifle, but if you’re not counting ounces, you’re going to be crying over pounds.

    Two quick question.

    How does the pencil barrel stand up to extended firing in terms of group sizes?
    Does the MPX use a standard AR-15 trigger group and channel that would allow the addition of an after-market trigger?

    From an personal appearance standpoint, I had hoped that they would include a third safety position marking for those of us who still hope to get drop in auto modules legalized inside our lifetimes, but that’s a minor quibble. (I don’t cry too much about lacking said markings on my DMR.) Fun fact, you can very easily build a drop in “giggle switch” module along the same lines as a modern drop in trigger pack. The engineering is not hard and most 5.56×45 carbines would greatly benefit from the addition of such a module.

    • Great point with pencil barrel. MCX will go against HK416 and SCAR-L in the completion to replace FAMAS in French military and I bet that they will test intense fire capabilities. Especially full auto

    • Apparently the trigger is the standard AR-15 trigger, so that can be swapped. Sucks for $1800+ you still need to do so, but that is life. Also, I would be surprised if someone didn’t make MLOK guards for the rifle once it becomes popular/Sig will release them once the rifle gains some market steam.

      • Still not a huge fan of pencil barrels. I’d really like to see what it does to your groups once the barrel heats up.

        May sound contradictory, but a pencil barrel on a carbine seems counter productive. You might save a few pounds of weight, but you’ll lose a lot of heat resistance. Not sure that’s where I’d look for weight savings.

        • I disagree. Pencil barrels should work well, especially on the semi auto civvie version. I’m not doing a dozen or so mag dumps. Carbines just shouldn’t do that. I’ll take mine through a class and see how it works out.

        • @Dracon1201

          Even one mag dump will start to noticeably heat an AR barrel. That can produce POI shifts and other weirdness. I’d really be curious about what you get when you run it through a good set of rapid fire drills of a 3Gun course of fire.

          As for a carbine not being “supposed” to do that… Don’t forget that excessive heating will cause your rifling to wear faster and can walk your gas block and upper receiver mounts loose. I always build my guns for a worst case scenario. There’s a reason why my little 10.3″ SBR weights in at 8.5 lbs with optic.

        • With regards to the “pencil” barrel. MOST aren’t going to be doing multiple mag dumps with this thing and if you are doing multiple mag dumps you’re probably not going to be shooting 1 MOA anyway with or without a heavy barrel.

          How many guys complaining about the thin profile have “M4” or “Government” profile barrels on their other rifles? What’s the profile look like under the hand guard? Yeah the Army wants heavier barrels because they want their carbines to be LMGs. Again, MOST civilians aren’t going to be doing mag dumps with these things AND be worried it’s not shooting 1 MOA.

          With all things, there are trade offs. I’ll happily take a pencil profile that shoots straight with low volume fire.

          BUT, it’s America so you can buy whatever you want… or not.

  4. I reorganized the ol’ safe this weekend. Rifle rods are great things … Oh, Hi honey, I didn’t hear you come in. Oh, nothing, just reading a website…

    • Yeah, at this point my wife would be like, “that’d better be porn you’re look’n at over there…not another gun purchase.”

  5. I’m with uncommon_sense on this one. I have no doubt its a great gun, it looks awesome. But I can’t justify spending over $2,000 on a rifle+trigger upgrade when I can get or build one for a little more than half that, trigger included. Don’t get me wrong, I’d love to have one, but not for that pile of cash. I’ll wait for an improved MPX instead.

    Good review Nick

  6. “Barrel changes are easier than coming-up with a metaphor for something easy”

    Best TTAG review line I’ve read in a while. Lol!

  7. I’m disappointed by the lack of ambi bolt controls, and the fact that the charging handle isn’t interchangeable with standard AR parts. I was really looking forward to decking one of these out with a Raptor.

  8. One interesting thing occurs to me. How are the ergos on that stock? It looks to me like you’re snuggling up to a piece of rebar.

  9. “The set-up also means the hand guards can be a tiny bit wobbly”

    This is worrisome when your front BUIS is located on the aforementioned “wobbly” part. “wobbly” makes it damned hard to hold a zero.

    • The top rail (where most mount their BUIS) is attached to the gas block and not part of the easily removed section.

      • The handguard is Not attached to the gas block, and there is No “wobble” in the handguard. I have one and absolutely love it, best rifle I’ve ever owned, and I’ve owned a lot. BTW, my trigger is the best AR type trigger I’ve ever had. Maybe it’s a fluke, idk, but being the type to change triggers right away I see no need to change mine.

    • It’s not “wobbly”. Pick one up some time and you will see. If you really put a lot of force into it, you may be able to slide the hand guard fore and aft by a couple thou. I would challenge anyone to see any perceptible POI shift using the BIUS sights. Shooting with the sights will be well within the margin of error for your eyes and any iron sight. Can you shoot under one MOA with any gun using iron sights? I can’t. But the MPX can with a decent optic and quality ammo.

      The hand guard/receiver rail is machined so precisely on my rifle that you have to take a lot of care to line it up and put it back together. Same with the fit between the upper and lower receiver. Snug. Accurate machine work everywhere.

      I shoot a 4X ACOG on my rifle anyway. Most likely will never need my BUIS. But if I do, they are there to be used for exactly as they are intended, BACKUP.

      This is a 6 pound rifle (before you start hanging stuff on it) with a feather weight barrel and a folding skeletonized stock. It folds up nicely to fit in your safe or in your vehicle. It is light, handy and makes an excellent patrol rifle, squad level weapon, and/or home defense weapon. It is not a Special Purpose Rifle intended for the Designated Marksman. If you want that, look at Larue OBR, Knights Armament, etc. Get ready to pay twice the cost over the MCX.

      However, with a cool barrel, match grade ammo, and a 4X optic, I have easily gotten 5 shot sub MOA groups and some 3 shot groups that were touching. Yeah, a feather weight barrel on a piston gun heats up quickly. But even with blinding mirage coming off the barrel/suppressor, I can still manage to keep 100 yard groups under 1.75”. PSSST: It shoots better than my Colt M4.

      The relatively high comb on the stock allows for a decent cheek weld. Again, much better than the factory stock on the M4. No, it is not a McMillan A5 or a Magpul PRS but, those don’t fold. The stock on the MCX is solid, precise, and has zero play in it. I like it.

      A couple of issues:

      1. Less than desirable factory trigger. Easy fix. Replaced it like I have on all my AR’s. Who has a decent factory AR trigger?

      2. I have yet to find a good way to mount my Surefire muzzle brake/adapter to the end of the tapered barrel. The 90 degree surface on the adapter does not mate up with the 45 degree surface on the barrel. After about 2 magazines, the adapter works loose. The crush washer and shims are deformed by the “cone”. Still looking for a solution here. So far this has completely blown the mind of everyone at Sig, Surefire, and anyone else in the gun industry. I don’t want to have to buy a proprietary Sig suppressor for the gun.

      Hope this helps.


      • I wish I read this before I ordered a Surefire muzzle brake for my MCX 300blk … damn it all..

        • I am sure any decent gunsmith/machinist can make an adapter for it. The gunsmith I use said he could cut the barrel at 90 degrees and re-thread it, no problem. I have not had time to do it yet.

  10. Isn’t pencil profile barrel gonna melt during full auto? I’m saying that because SIG Sauer wants MCX to go against HK416 and SCAR-L in that completion to replace FAMAS in French military and I bet that after G36 fiasco they will test intense fire capabilities

  11. The price I found isn’t near MSRP ..
    Yes , after market AR triggers fit ..
    My trigger is about 5 lbs. With no creep and clean break ….
    Front sight stays on even with the little flex in handguard …
    My biggest complaint is the 1:7 twist .. I’d rather seen a 1:8 ..
    It doesn’t like 55 gr. Factory ammo ..
    It loves 75 gr. H Match , shot right at MOA @ 100 with a EO ..

  12. “there’s one major difference: it’s gas operated.”

    AR-15’s are most certainly gas operated as well. The above text implies that they are not and that the key feature of the MCX is that it IS gas operated.

  13. Why a 1/2 star reliability knock for the crap reloads? You show in the picture that the rounds are clearly not to spec. Saying that the rifle is better with ammo that has properly shaped brass isn’t the fault of the rifle. Just curious.

    • “reloads I picked up at the local gun range for a few pennies a round.”

      I suppose if you skip the resizing die, it would cut the cost a bit.
      Gotta wonder what other steps were skipped – like calibrating the powder drop.

      I wouldn’t shoot ammo like that if it was free.

      • Exactly my point – there are reloads and then there are “cheap reloads” – big difference between a micrometer die-seated 77gr SMK match handload and Billy’s Bargain Bin mixed headstamp loads using who knows what powder and equipment?

        So again, why knock a half star off reliability when a rifle refuses to chamber improperly loaded, potentially unsafe ammunition? Especially when Nick states it failed to run in the PWS, a known ammo digester?

        It’s no big deal either way I was just curious.

  14. Doesn’t being piston-driven introduce more moving parts? More things to fail?

    Pencil barrels are great for being lighter, I suppose. Isn’t the benefit of a thicker barrel that it holds its shape better under the high temperatures of rapid fire, and therefore maintains acuracy? How well does this pencil barrel hold up and perform under those conditions?

      • I could see that, ceteris paribus; that is, other things being equal. However, other things are not equal.

        High temperature can lead to barrel deflection, or bending,which can impact accuracy. Insofar as heavier, thicker barrels can absorb more heat and resist deflection, then they’re more accurate than lighter, thinner barrels in that regard.

        You’re right, though, and I agree, that there are many other barrel factors that affect accuracy (barrel design, materials, workmanship, etc.) So it would not be fair to declare a given heavier barrel as being more accurate than a thinner, lighter barrel, because there could well be other factors involved affecting both barrels’ accuracy.

        It’s all mostly moot, anyway, and a typical shooter’s gear is usually far more accuracy than he or she is.

        • Barrel stiffness has a lot more to do with accuracy than thickness – but you’re right, two barrels made in the exact same process the heavier barrel would be more rigid and therefore more accurate. I’d imagine SIG knows what they are doing here since this is a civilian version of their select-fire rifle, but I doubt that rifle going to trials will have this 16″ barrel.

  15. Ok, full disclosure, I love SIG products, but I thought the rule was 1 MoA for 1k$, reviewed as is, not as could be. By that metric, would this gun still be 4 stars?

  16. The top round that failed to load looks as tho there was too much lube on the die when the resizing was done.

    The other one was dropped or dinged somewhere.

    Both should not have gotten into a batch of loaded ammo for sale.

    • The bottom round looks like what comes out of my SIG556 SBR, if I can find the casing after it returns from orbit.

      Needless to say I just throw them out, and save the LC brass for reloading for the ARs.

  17. If you could hear me right now you’d hear a joker laugh. Sig decided that the only way to fix the AR15 was to turn it into an AR18 hahahahahahahahahahahahahahaha.

      • US military’s mistake? The US military’s mistake is not teaching the basics of how your rifle works and to maintain it, and unit armorers caring more about the weapon being carbon free than actually replacing the parts that need replacing.

  18. I wish I had the same luck as Nick.. I “had” first gen 300blk with the 556 barrel. First 2 shots and the rifle failed on me. Did I mention I used Sig Sauer Factory 300blk ammo? That was 5 months ago I still don’t have my rifle back from Sig Sauer.
    Nicks overall impressions are on par on what I say about the platform well balanced and easy to use cause of the AR style controls. Serviceability is unrivaled to anyone other weapon platform out.
    Yes I believe the platform is great but bringing the platform to market with a weak support from the factory will bring my business elsewhere. Email me Nick and I will show you pictures of the failure.

    • I saw the MCX in 5.56 at a local sporting goods store called “Gander Mountain” in late December of ’15. I loved it when I handled it. My local gun shop “Bullseye” stated they didn’t have one in .300 BLK but they had the “MPX” in 9mm – that was a cool short barreled “rifle.”

      The MCX has been out for some time now. I asked the salesman if the MCX could be obtained in .300 blackout. He said “not at this time.” To “Wolly’s” comment about waiting for the .300 BLK, I called Sig and the rep said .300 is “not shipping anytime soon.” I’d get one today if it were NOT 5.56 as I wanted the .300 BLK. It’s also not out with Russian 7.62 x 39 either. Sig gave no reason why – remained elusive. Maybe they are having issues with 300 BLK. (Rajahat)

      I remember waiting years for the H&K MR762 (.308) that took forever to ship. Rumors swirled about that rifle’s “problems” but they seemed to be rumors and I eventually became disinterested especially when the price stayed at @$4k with no BUIS and ONE 10 rnd mag – lol!

      I hope Sig will get this rifle’s other calibers produced as we approach a year now of it being shipped. Seems like a great rifle.

      Thanks for a good review by Nick Leghorn and follow up by “Woolly.”


  19. I have an AR-15 with a CMMG .22 conversion kit. It is the only way I can afford to shoot it. With most guns of this type, and even large caliber handguns, it is easy to go through more $$$ in ammo than the gun itself cost in a very short time. The Sig is a beautiful rifle, but I can’t afford it, nor can I afford to shoot it.

  20. Gorgeous gun and nice review. Sadly, andy cuomo has deemed all guns that look evil forbidden in NY. In fact, he’d most likely soil himself if he saw this thing inside his empire…um, I mean…The Empire State.

  21. So the gun is sub-moa while having a bad trigger, piston, pencil barrel that is easy th change….where is your god now?

    • Yeah… If you cherry pick your data and fire only four (five) rounds. There is nothing inherently wrong with a pencil barrel for a recreational gun. Calling this thing “sub moa” is, at best, disingenuous. Fire two to three hundred rounds in a half hour, then try to hit a six inch plate at 300 yards. Good luck.

  22. Nice job, Nick! I liked the hell out of the SBR I shot in New Hamster, and I pushed them really hard to get me a 5.56 so I could run it in a 3-Gun match last weekend. As you may have heard, I promptly slagged my right knee…literally. Hell, I can’t drive or sit in the passenger seat or fly, much less run and gun! LOL! The MCX set up with one of the new Trij MROs, is sitting in my gun safe. I should have a shooting bench delivered in the next couple of days, so I can do some accuracy work.

    I love the way the gun feels…hard to explain, but it seems to handle as good as my high end JP ARs with less weight. I’m gonna go ahead and buy the gun and add a SIG suppressor. My initial plan is to run it in 3-Gun next year (oh please, God, get me on my feet by next summer!).

    It’ll probably be SHOT before we talk in person, but I would like ask you if you’d like to be one of our expert on GUN STORIES WITH JOE MANTEGNA.

    Thanks, brother…

    Michael B

  23. Love this purchase. Having trouble finding a 9″ barrel conversion kit; the 556 Sig Suppressor goes into production 11/2015…have one ordered.

  24. I see it as a pretty darn good rifle.. Most, 99% , wont use it for battle.
    So, as a range, practice SHTF gun, is it worth it? Well, if it fires everytime, then yes.

  25. Hello everybody

    1. Excuse my bad english! I’m from Switzerland 🙂

    2. Very good report!

    3. I have to buy a new rifle in front of me. The choices are:

    SIG MCX or HK MR223 (in Switzerland are only the zivil version legal)

    Seeking a gun which is designed for the tough conditions and is maintenance-free as possible. I am not a collector. The rifle is shot on the range and on the field, it we be delivered dirt and water. Seeking a rifle that for future situations in armed Eurpoa is :-/

    Which model do you recommend me? SIG MCX, HK MR223 or something completely different

    Many thanks and Christmas greetings from the land of chocolate 😀

  26. I ordered the .556 MCX and it is scheduled to deliver on December 7. I can’t wait to shoot this rifle. I preordered the 300 blackout conversion kit and 9 inch barrel directly from Sig Sauer. The 300 blackout kit will not ship until late 1st Qtr, 2016.

    • I heard the same as of today (1/13/16). Barrels will be available in 1Q 2016 late. As long as they ship them and they’re reasonable $

  27. I have had my MCX for a few weeks now. Paid $1600 for it. Ordered a Geissele SSA-E after my first range session. I love this little carbine! I have had no problem shooting Sub MOA 5 shot groups with a variety of my handholds. My hand loads are NOT crappy. I mounted a Trijicon ACOG TA31RCO Marine Optic 4 X 32. A great combination.

    So far the rifle has eaten every thing I have thrown at it. No failures of any kind. I have had some form of AR-15 rifle since 1982. This is my first gas piston operated. So far, this is my favorite carbine. Groups are almost half of what my Colt M4 LE6920 will do. Its lighter and runs cleaner, and has adjustable gas block for my 5.66 SOCOM suppressor. Comes completely apart in in seconds for thorough cleaning (including the piston).

    My Larue OBR 20” will out shoot the MCX by a wide margin but, that SPR type gun is twice as heavy and considerably more expensive. I keep a SureFire mini Scout mounted on the MCX for a handy home D weapon.

    I have owned a Noveske Gen II, and have quite a bit of trigger time on Daniel Defense as well. The MCX is as good or better than any other carbine out there.

  28. Wow, great article! My MCX should be here in about 4 weeks. Sounds like you’ve expended a lot of time and effort with this evaluation and have been very objective in the process. I’ve also read a few other articles about the trigger issue, however, have found it difficult to get any concise recommendations on where to find some aftermarket drop in trigger choices.

    If you (or anyone) have any recommendations, please pass them along. Again, GREAT job on you MCX article.

    • Trigger? Easy. Geissele. I have the SSA-E in my MCX, MPX, and Larue OBR. There are several good triggers out there on the market. Of all that I have ever owned or shot (in an auto carbine), The SSA-E is my hands down favorite. These triggers are light, crisp, accurate, rugged, and backed by Bill Geiselle’s life time warranty.

      If you want a little heavier pull, get the SSA. I have a Jewell in my Colt LE6920 and don’t like it. It is just too light for a defensive carbine. I can tighten the adjustment screw all the way to the point it won’t reset and it is still too light.

      For all those who whine about the price and not getting a great trigger with it; I have never ever bought a factory gun in my life that had a decent trigger, regardless of the cost of the weapon. After the Remington debacle, all of them have “lawyered up”. Might as well get used to the idea.

      You are going to love your MCX Dave. I can’t wait until Sig gets the 300 BLK conversions to market..


  29. Follow up for the MCX by someone who actually owns one:

    After a month or so with the MCX:

    BUIS on the hand rail: It’s not “wobbly”. Pick one up some time and you will see. If you really put a lot of force into it, you may be able to slide the hand guard fore and aft by a couple thou. I would challenge anyone to see any perceptible POI shift using the BIUS sights. Shooting with the sights will be well within the margin of error for your eyes and any iron sight. Can you shoot under one MOA with any gun using iron sights? I can’t. But the MPX can with a decent optic and quality ammo.

    The hand guard/receiver rail is machined so precisely on my rifle that you have to take a lot of care to line it up and put it back together. Same with the fit between the upper and lower receiver. Snug. Accurate machine work everywhere.

    I shoot a 4X ACOG on my rifle anyway. Most likely will never need my BUIS. But if I do, they are there to be used for exactly as they are intended, BACKUP.

    This is a 6 pound rifle (before you start hanging stuff on it) with a feather weight barrel and a folding skeletonized stock. It folds up nicely to fit in your safe or in your vehicle. It is light, handy and makes an excellent patrol rifle, squad level weapon, and/or home defense weapon. It is not a Special Purpose Rifle intended for the Designated Marksman. If you want that, look at Larue OBR, Knights Armament, etc. Get ready to pay twice the cost over the MCX.

    However, with a cool barrel, match grade ammo, and a 4X optic, I have easily gotten 5 shot sub MOA groups and some 3 shot groups that were touching. Yeah, a feather weight barrel on a piston gun heats up quickly. But even with blinding mirage coming off the barrel/suppressor, I can still manage to keep 100 yard groups under 1.75”. PSSST: It shoots better than my Colt M4.

    The relatively high comb on the stock allows for a decent cheek weld. Again, much better than the factory stock on the M4. No, it is not a McMillan A5 or a Magpul PRS but, those don’t fold. The stock on the MCX is solid, precise, and has zero play in it. I like it.

    A couple of issues:

    1. Less than desirable factory trigger. Easy fix. Replaced it like I have on all my AR’s. Who has a decent factory AR trigger?

    2. I have yet to find a good way to mount my Surefire muzzle brake/adapter to the end of the tapered barrel. The 90 degree surface on the adapter does not mate up with the 45 degree surface on the barrel. After about 2 magazines, the adapter works loose. The crush washer and shims are deformed by the “cone”. Still looking for a solution here. So far this has completely blown the mind of everyone at Sig, Surefire, and anyone else in the gun industry. I don’t want to have to buy a proprietary Sig suppressor for the gun.

    3. Still waiting on 300 BLK conversions.

    Hope this helps.


    • Dave,

      I got my MCX today. I called my dealer this morning and they said they had both the 5.56 and 300 AAC in stock. Last week they didn’t have ANY and weren’t sure when they would become available. I am beginning to think the industry is keen to the hype and keep us all guessing so the profits stay high. Who knows.

      Regardless, I chose 5.56, not my fav cal, but I can score ammo cheap. I hope I made the right dec. The salesman had “no idea” when the barrels would ship nor did he know the price. Guestimates today ran about $350-400. I was told they’ll ship late 1st Q ’16. My other choice was the SIG 716 18″ bbl – more power and .308 can be had as easily as 5.56/.223. They didn’t have the 18″ bbl.

      I also got the SIG .308 can. In case I swap calibers, i’lll be covered. Gonna pick up some ammo and shoot next week. I’ll keep y’all posted. Thanks!


      • thanks Rick. My LFFL just called. my MCX came in, will pick up later today (1/13). I hope you’re right and the 556 and .300 barrels are more like $350-400. My last chat with SS CS said they would be $750 ouch.
        Time will tell. I’ll also submit range report in a couple of weeks.

      • Rick,

        Which can did you get? I have been looking for the 5.56 Titanium Direct Thread but they are not out yet.

        • Woolly,

          I got the “SIG SRD762Ti-QD Rifle”. It’s approx 8″ long and retails for $899. I paid $800. It’s Titanium supposedly. I chose this one for its light weight and its ability to handle many calibers – should I ever want to swap barrels, i’m covered.

          Cals include: 5.56, 300BLK, 762 Russian, .308, and 300 winny mag. It just screws onto the end of the tapered barrel on my MCX and clicks and locks in. It’s so easy to use. The process to obtain one is lengthy.

          Shop around for a deal!

          – Rick

        • Yeah I see a lot of the Sig QD suppressors out there but none of the direct thread taper locks. I was at my gunsmith’s shop today and he said he could square up the end of the barrel on the MCX no problem. That way I could use my Surefire SOCOM and adapter that I already have in my possession. He could also cut the barrel down and pin the adapter for an overall barrel length of 16″. Makes it a couple inches shorter without having to do a Form-1. That is probably the route I am going to go. That SOCOM is a great suppressor too.

          Congrats on your new rig! How cool is that?


          • Woolly,

            That SIG .308 can I bought was really light weight. Suposedly the can just screws onto the end of the barrel and then it clicks and locks itself in. It has a thumb lock. It’s a quality piece and mates easily because it’s from SIG.

            The SOCOM can you mentioned is a awesome unit – very well made – great supression and wow costly! They make a Ti version in .338 Lapua (SIG has .338 too). The SureFire is the best out there and it won’t affect accuracy. Not sure of SIG will affect anything but i’ll get back with my results. I compromised on cost going with a SIG can to save up for better glass.

            I had to fill out that Form-1 as you mentioned.

            I thought freshening up my Garand was expensive – and it has no scope on it! My SIG is already at $2600 without glass. It’s all good though. I love this MCX!

  30. As of 1/18/15, you can get the MCX in 5.56, with the 300BL conversion kit (16″) for $1900 on Gun Broker.

    If you wanted to get just the 16″, 5.56 model in this review, I’ve shopped around and the average price is about $1650 to $1700.

    Then if you want to buy a 9″ 300BL barrel conversion kit (or, any caliber conversion), then you can order them separately. The 9″ 300BL conversion kits are currently on back order from Sig. for $599. It’ll ship 2 to 3 months after you order it, and you won’t be charged till it ships. I don’t know the price for every conversion kit, but I’m assuming that the SBR barrels are the most expensive, just as the MCX models get more expensive as the barrel gets shorter (supply/demand).

    • Thanks Rick!

      Wish the MCX with both barrels were available when I picked up my rifle a week ago! Damn. I did find cheap .223 plinking ammo at @.23c per rnd. at “Lucky Gunner.” BTW, I paid $1500 for my MCX.


      • I too just bought a 1000 from Lucky Gunner. I got the Federal with brass cases so I can reload them. A little more costly 32c/round. But should get good use out of the brass.

        Also have 500 rounds of M855 109 in stripper clips on back order at Midway.


        • Woolly,

          I have a bunch of .30-06 ball ammo left over for my Garand. I’m not shooting it. Why is ammo so expensive? 30-06 and .308 have been out forever. 5.56/.223 isn’t too bad but 300 AAC is over .80c/rnd and we’re out of the drought too. Geez

          • Man I know. So glad I reload! Cuts the cost by 2/3 rd and I can load quality on par with all the premium brands. 223/5.56 is kind of a pain to load so sometimes I just get some bulk. I had rather be shooting/training than standing over the “one armed bandit”. But, for precision rifles, I roll my own. It’s also a good hedge against the dreaded droughts.

            I have a couple of the 3Bucc brass catchers to coral the brass from automatics. Helps a lot.


        • Woolly and Rick would you recommend the MCX over the 556xi?? I haven’t followed too many reviews on the xi. I do have an old 556 swat that has been flawless. I can’t get it to malfunction even when trying to intentionally. I have shot well over 5000 rounds without a single hiccup and as of late I have been intentionally not cleaning it but it just runs and runs and runs spitting out brass and even cheap steel case. My only complaint has been how heavy the gun is. I was looking at buying an xi but now can’t decide between that or the MCX. Your reviews have me leaning toward the MCX. Thanks!

        • Josh,

          I have no experience with the 556xi. What attracts me to the MCX is the ability to change barrels/caliber’s quickly and easily and how light and compact it is. I have a 9″ 300 BLK barrel on backorder from Sig. I also have a SRD762Ti suppressor purchased from Silencer Shop and waiting on stamp from the BATFE.

          Sig has no estimate on the barrel. Also, I am not even able to backorder the hand guard that fits over the 9″ barrel and the suppressor. So who will get their act together sooner? The Feds or Sig? We will see. I guess there is no advantage to anything you cant get.

          I put about 100 rounds through my MCX last week when I swapped scopes. This is my first piston gun and it amazes me how clean the BCG stays. With only 100 rounds, their was no need to clean it.

      • Woolly and Rick would you recommend the MCX over the 556xi?? I haven’t followed too many reviews on the xi. I do have an old 556 swat that has been flawless. I can’t get it to malfunction even when trying to intentionally. I have shot well over 5000 rounds without a single hiccup and as of late I have been intentionally not cleaning it but it just runs and runs and runs spitting out brass and even cheap steel case. My only complaint has been how heavy the gun is. I was looking at buying an xi but now can’t decide between that or the MCX. Your reviews have me leaning toward the MCX. Thanks!

  31. I have owned both and the MCX (for me) is a FAR better choice, however, do your due dillegence / research and make your own decision.

    • Thanks for the replies! I think I’m going to go with the MCX in 300 blackout and get a 556 barrel for it, maybe SBR it and suppress it down the road. MCX appears to be having great reviews and 556xi looks to be having hiccups.
      Woolly, I only have one DI AR that I built about 10 years ago using a LMT lower and a Troy Ind upper. It has been a great rifle, but everything else is gas piston for me. SCAR 16 and 17, LWRC M4, SIG 556, Bushy ACR and looks like I will be adding an MCX to the family.

  32. JoshC,

    I’d advise to get the MCX. IF you’re gonnna shoot 5.56, the MCX is more than competant. It’s so well designed, modular and light. You’ll be surprised at how light the rifle is at 6 lbs. When I first held it, its weight reminded me of an air rifle but build quality is evident immediately.

    When you add the 30 rnd mag and some glass, it’ll gain some but it feels balanced because the scope is centered. I shoot 20 rnd Pmags when i’m using the bench. But the 30’s allow me to shoot without reloading as much. They’re shipping them now with the 300 BLK barrel and 5.56. IF I had that option, i’d have taken it.

    SIG makes cans for them that fit easily on the threaded barrel. Takes about 5 mos. to get the OK from ATF.

  33. Thanks Rick, I am pumped for this rifle. What do you mean they are shipping them now with 300 BLK barrel and 5.56?? Do you mean you can order them with both barrels together as a package deal? I will definitely be running it suppressed. Are the sig cans quality? I have a silencer co can that is pretty good. Do you know how much the 5.56 barrel would cost if I went with the 300 BLK? Thx

    • Sig is now shipping the MCX – (Second Gen model) with adj. gas reg. Original MCX had auto regulating system that in 300 BLK was reportedly short stroking where bolt was not locking back. Who knows if it was an isolated ammo problem or a real mechanical issue, SIG decided anyway to ship the rifles with a manually regulating system. So far no reported problems.

      I picked up my rifle last month in 5.56 literally days BEFORE SIG began shipping them with both 5.56 and 300 BLK barrels. Someone posted here that the 2-barrel option costed only an extra $300, a real steal IMO. I recommend you get both barrels since it’s so cheap and the MCX let’s you swap either out so easily.

      The SIG cans IMO are good quality. No one has yet compared them to an industry leader such as the Surefire SOCOM units. SIg makes their cans without an outside shell because their welding process makes them rigid (according to SIG), so they are lighter than some. The can simply twists and locks on. It takes @5 mos to get the supressor because the BATFE goes through your paperwork. Whatever.

      I was formally looking for a .308 piston rifle and got tired of the delays and the escalating prices. I never thought I’d consider 5.56 but the well thought-out modular platform design in the MCX, that offers 2 other calibers designed with supression, influenced my decision.

      • Good stuff, thanks for the input. I have it direct from Sig that the 5.56 barrel has an estimated ship month of April and the retail will be $599. Back orders can be called in now.

        I’ve only had one range visit with my MCX .300 Blk and Sig CP4, however I’m thrilled so far with its performance. Installed the Tele/Folding optional stock yesterday, will report back on that after my next range trip. I have some reman .300 Blk ammo coming in the mail (at .47/Rd ) and will report the results of that also.

  34. Forgot to mention, I’m running a Geissele GS2, #05-145 and it feels and operates much better than the stock trigger.

  35. 26 rounds in my MCX straight out of the box from shoot straight in Lakeland Florida and it blows the buffer springs into three pieces and seized my t handle. Not what I wanted from my first SIG!!!!!!

  36. I’m sure u already know this but, I’d call SS and get a downloaded shipping label, etc. they will fix it and return it w/no shipping costs.

  37. Well I wish I would have researched the mcx a little more. Just spent $1700 and now I’m worried I made a bad choice. Really stuck now so I hope not. I was going to but a colt and I’m hoping I didn’t just buy a $1700 boat anchor.

    • Why? It is a great rifle. I have had zero issues with mine both suppressed and unsuppressed. Mine has the adjustable gas block. Also shooting it with the excellent SSA-E trigger.

      It will outshoot my old Colt LE6920(sold) but not my new LE6040.

      Just don’t count on getting any conversion kits anytime soon. You’ll love it!

      • Woolly,

        I took your advice and installed the Gisele SSA-e trigger in my MCX 5.56. Wow what a difference. Thanks for the heads up. It’s a great trigger and recommended.


  38. Why would anyone buy this in 5.56? It’s like buying a revolver to shoot .45ACP. The whole concept was suppressed subsonic 300 AAC.

    • Chris,

      I got my MCX knowing Sig was going to ship 300 BLK at some point. As you said, I didn’t want 5.56 but wanted the 300 BLK to use suppressed. I hear the barrels are not shipping as promised. Has anyone gotten theirs with the two barrel option? It’s a great rifle regardless of caliber.


  39. I bought the MCX 5.56 last year on the promise of a 1st quarter 2016 availability of the barrel kits. Not to be! Even the 300blk barrel kit is another 6 months out unless you purchased the Cabela’s rifle that came with the 5.56 and 300blk. The 7.62×39 is why I bought this rifle and it appears that no one at Sig knows the release date of those kits. It appears as if Sig has dropped the ball on this, and it’s upsetting. I didn’t ‘need’ another 5.56. The “first quarter” promise was evidently a marketing scheme to encourage purchases. Pretty sorry if you ask me.

    • I feel your pain. I got mine over six months ago too (5.56 carbine) with the intention of converting to 300 BLK SBR.

      I have had my approved Form 1 and Sig suppressor now for a couple of weeks and still no estimate for the 300 BLK 9” conversion kit. That sucks.

      Yes it is a great light weight 5.56 carbine but I did not need another one of those either. My Larue and LE6940 fit that role perfectly.

      Now I would hope that Sig is so busy filling massive orders to the Military and law enforcement agencies of the world that they just can’t keep up and they are not like most American manufacturers these days that are flat of their arse.

      I would also hope that in the near future, these fine weapons will be as common as the LE6920, etc.

      Why would I buy a 5.56? The 300 is and has not been available.


  40. I wish writers and posters would actually try to understand different trigger types, weights, etc. Why are there so many negligent discharges with glocks? Part complacency, sure. But a vastly different philosophy. Im on the sig side, as in a gunfight, i want a heavier trigger.
    About “pencil” barrels, they work fine. Unless you will be in a 10 mag or more firefight, you dont need a heavy barrel of any type, m4 cut or not.
    Learn a bit about the WHY a given manufacturer chose what he did.

  41. At $1900 this gun is way overpriced. You can buy a factory Colt 6920/21 and a gas piston kit for less and have a far better rifle. The only AR-15 I’ve paid $2k for was a Rock River Arms loaded with options including a SureFire M951 Light System, SureFire M73 Quad Rail, EOTech 552 Holosight ($600 alone), GG&G Flip-up Rear Sight, Viking Tactical VTAC Sling, 6-Position Tactical CAR Stock, National Match RRA Two Stage Trigger, Chrome Lined Wilson 16″ barrel, and more. So much more gun for the money. Besides, spare parts for AR-15’s are so easy to come by. Why stray away from perfection and take all that risk and get slammed in the wallet at the same time?

    I own 13 AR’s and a COLT M4 among dozens of other guns. I highly recommend any newbie to talk to their gun savvy friends before dumping anything approaching the cost of this gun on this experiment.

    If you go with a low cost AR15 you could buy three of them for the cost of this one gun.

    • Juna,

      I shopped around for my MCX and got it for $1500 in Jan (without the second barrel). You can find them for around what I paid. $2k is a lot for a 5.56 AR I agree.

      After the Orlando incident, I wouldn’t be surprised if prices went back up as the waiting list gets long. AR’s are selling like crazy right now. Some dealer said he was selling 15 AR’s per hour. I just scored some ammo. With the bickering by the left in DC, it may not be too long before perhaps we have an ammo shortage again.

      PS: Found an MCX with both 5.56 and 300 BLK on Gun Broker for $1899. That’s not bad for a two barrel rifle.


  42. here’s an wild concept: if you find that a particular item is overpriced for your taste and/or budget–don’t buy it. I know, it’s strange, but it’s a wonderful country, don’t you agree?

  43. Just bought the MCW in 300BLK with full-length barrel from Cabelas. Intending to interchange the upper with my M16 lower and a 9″ barrel+gem tech suppressor, which I already own. Really liked the idea of the suppressor inside the full-length hand guard, but the hanguard is too narrow for the can by just a bit (maybe .125″ or so). I really don’t want to have to get another 30cal can, so I’m looking into how to modify the hand guard somehow to fit the can I have. Best laid plans… But wouldn’t you think a little extra room would have been provided, given all the great photos of that setup?

    I haven’t fired the rifle yet, but fit and finish is typical SIG, and the trigger’s about par for a GI AR. When I get optics on it I may upgrade the trigger as needed.

    • I guess you meant MCX not MCW?

      The MCX upper will fit on a M-16/AR-15 lower but, there is some kind of adapter that is required to keep it from beating up the buffer tube on the AR. Two totally different animals there. There are a few YouTube videos out there on the subject.

      Sig barrels are “coned” at the muzzle. I had trouble finding a way to get any adapter to stay tight and in place to mount up my Sure Fire SOCOM or AAC 762-SDN-6. Sig, AAC, and Sure Fire were clueless on the problem and offered no solutions. I broke down and bought Sig suppressor that is designed to mate up with the Sig barrel. Stamp should be in any day now. That sucked. I really had planned on using my AAC can.

      As far as using a 9″ barrel, I am sure you know that it will have to be a Sig proprietary barrel. I have had mine on back order now for 9 months. My Form 1 is already approved but no barrel in sight. But when you order the barrel, go ahead and put an order in for the oversized hand guard as well. Same story. Backordered for eternity.

      I guess it will be great some day when Sig gets their feces consolidated and gets the promised products to the customers. In the mean time, I have a great little carbine with a 16″ 5.56 barrel, and a 16″ 300 BLK barrel.

      Best of luck,

      • Woolly,

        My gun shop said the same thing last week. No other barrels are being shipped for my 5.56 MCX. I got my SIG can but that’s as far as i’ve gotten. When I scan their website, it seems many things are “out of stock” or on backorder.

        I picked up a different stock for my rifle, a longer telescoping version to accommodate the reach of my long arms. My gun shop had it right there but SIG has it on backorder! I’ve also been waiting for the barrels now since early Jan ’16.–MCX–MPX–SIG-FOLDING.aspx

        The MCX is a great rifle. The Geissele SSA-E is amazing. Thanks!

        – Rick

  44. I don’t know why people are rag ‘n about the trigger; I just picked up an MCX (16″ barrel) added a Sig Romeo 7 red dot, burned about 500, 5.56 PMC X-TAC 62gr Green Tip’s and I’m shooting really tight groups, you all must have fat fingers… I can practically right my name with it at 100 ft. Lol. I just purchased the 7.62 can so in about 6 months when the stamp finally gets processed… I’ll go ahead and buy the full .300 BO upper. Oh, and did I mention this gun is really fun to shoot!

    • You’re one of the lucky ones then. The spec for the trigger is pretty broad. The one I tried was worse than any trigger on any gun I’ve ever encountered – including double action pull on out of the box revolvers.

      • Your right, I just changed the trigger to the Geissele Super Select-Fire SOPMOD (SSF) and it’s frigging awesome!!! Was shooting tight groups before with the Sig MCX using the stock trigger and then noticed a few would be about 2-4 inches out of the group. I changed to the SSF trigger using the Romeo 7 red dot and now shoot more consistently. I don’t know whether it’s the short-stroke piston or what it is but to me it feels like there’s less kick with the MCX so it allows me to relax a little more and really drill in some 2 inch groups at 150 ft., the trigger bring it all together.

  45. The word is “than” and what it does differently is caliber conversions with multiple barrel lengths (SBR). Adjustable gas blocks for shooting super/subsonic ammo. No buffer tube so the folding stocks folds up into a much smaller compact package. Super clean. Easy to break down gas piston and all parts with nothing more than a punch, etc. Wear parts are all easily replaceable.

    Does the SCAR do all that?

    All the above assumes Sig ever gets the product to the civilian market of course.

  46. Picked mine up today from Cabelas. Great rifle. The trigger is your typical AR15 off the self trigger. Its typical. Any good after market trigger will make a vast improvement on any rifle. The rifle is super light! I’m going to get another one for the wife and two of the pistol versions for the kids. Those are 5.5 lbs! Great job Sig Sauer. For the few of you who complained about the price. Grow up and join the rest of us adults. Its as high dollar item because its worth it. Why do you think divorces cost so much? Because there worth it if your married to a biatch!

  47. The weight of a 556 Sig MCX with 16′ barrel is 6.9 pounds not 6!!! Weigh the rifle yourself, don’t just say what you are told!!! This is a request to edit the article and revise the weight. You should spare others from this misinformation.

    • Nathaniel, this article is correct. The weight you are referencing is the newer version of the SIG MCX with a heavier barrel.

  48. I bought the rifle in .300 and was intending to use the upper on my M16 lower with a 9″ barrel. However, several issues:

    1. The standard hand guard WILL NOT fit most standard .30 cal supressors inside. It’s about 1/8″ too narrow. So they made a special one you can buy ( for more $, for no good reason). OK I waited a year and a half for that. Turns out it is about 1.5″ shorter than the original one, which kinda defeats the purpose of covering the can, even with a 9″ barrel…
    2. There is also a part needed to use the upper on a standard AR/M16 lower (buffer stop, I think it’s called?) which doesn’t seem to be available yet.
    3. The recalled BCG exchange…
    4. Each transaction has taken months, so now a year later I take it to the range to see how it performs. Can’t get it on an 18×24″ sight-in target at 100yds! It is all over the place. Also sighted in a rebuilt Garand from CMP for the first time in 4 shots and then put 50 rounds in a 6″ target with iron sights and bifocals. So what’s the issue? I’ve checked to make sure the screws holding the barrel connection aren’t loose, I’ve tried iron sights and a red-dot, and the rounds are all over the place with no pattern and no grouping. They are feet apart, at 100 yards!

    Not too impressed. Yes the trigger is shitty, and the cost was high to begin with (and climbing). The rifle looks great and fit/finish is wonderful, but the only thing worse than a rifle that doesn’t work is a rifle that can’t hit.

    • I finally got all my parts in as well, Sig suppressor, oversized hand gaurd, 9″ barrel. It is a great little gun and packs up very small (without the suppressor and short hand gaurd installed). Wish I could post pics here.

      Out of the box, you can expect equal or better accuracy of a Colt or any other comperable AR. The stock trigger is actually better than Colt. I replaced mine with a Geissele SSA-E, as I have with all my AR’s.

      I carry mine on my boat which takes me to the South TX coast on overnight fishing and hunting trips. Here one might incounter hogs, snakes, gators, and two legged illegal drug/human traffickers. In that role, I prefer the short barreled uncompressed configuration with super sonic 300 BLK 125 soft tips.

      At home, it is suppressed with subsonic expanding 220’s. I have a 16″ 5.56 barrel and a 16″ 300 BLK barrel as well. It was a long wait for me to get all the parts but I’m glad I did it.

      • Hey Wholly, it’s been a while. This blog was hijacked (lol). Wanted to compare what we said in 2015-2016 until now.

        Our 1st gen MCXs are apparently not supported by Sig. I tried for years to get a shorter 556 barrel kit (11”) and it was always “out of stock,” and dealers never knew when they’d come in.

        I spoke to Sig and they said my lower isn’t compatible with the 2nd gen Virtus uppers. Btw, Those Virtus uppers and other SBR rifles are also “not in stock.” It’s a similar play by them while they change the rifle, like they did to ours.

        I suspect they’re getting ready to maybe change the Virtus to something else as dealers still don’t know what’s going on (same as 2015-‘16). They’re blaming “supply issues.” What was their excuse in ‘15-16? Their website isn’t showing rifles they had last year. They’re very under the radar about it.

        I wanted a Sig lower that I could use with their current piston uppers in the future, so I called Sig to make sure that works. The tech couldn’t answer my questions. They’re emailing me later today with response. They never made the 762 Russian option (had issues) for our rifles and 300blk conversion kits were always ambiguous.

        Otherwise my rifle works great. Hope you’re well.

  49. viva sou mecânico de armamento da guarda nacional republicana(portugal) tive oportunidade de disparar com a SG.MCX 5,56×45, fiquei apaixonado ,e sem duvida uma das melhores ferramentas de trabalho que já testei.Pese o preço ,e uma arma a ter em conta para qualquer situação mesmo das mais complicadas .

  50. I received an unmolested MCX (pre-new BCG) and after just a little work, the thing is nothing short of amazing.

    Some guys want rifles that break down without having to pay their “slave stamps” for an SBR. Personally, having an AR with a LAW folder wasn’t sufficient for my needs, so I was forced to chose between the Bushmaster ACR, the CZ Bren S1, the SCAR 16 or the MCX. I chose the latter after firing all four.

    The trigger does suck out of the box. After the BCG swap, it became clear that claiming Geissele and Sig were working together to monopolize the MCX trigger game (as other triggers become unusable) would not be a far-fetched conspiracy theory.

    That said, I got around playing their game for absurd amounts of money by keeping the stock trigger and replacing the springs, opting for the $10 JP Industries 3.5 lb Enhance Reliability springs.

    Before the springs, the trigger would frustrate me during zero. After, I was hitting the “MOA or less” claims that Sig was touting. No failures with even the hardest of primers and the crappiest of steel cased ammo.

    The MCX has had some hiccups in it’s opening phases, much like a lot of things Sig US has pushed out. Personally, I blame Sig’s CEO. You can do your research and draw your own conclusions.

    That out of the way, the rifle is amazing and well worth your investment. Buy one, throw in the $10 for a spring kit and fall in love.

  51. Kills children in no time flat! Just what every home needs, you know to protect your family and your property! To really see the results, check today’s newsfeed!

      • Robert, “Shandra” is a Soros paid poster. The left is organized and well funded. Ignore “its” post. The moderator should have been aware of upcoming political posts regarding recent shooting.

      • Nonsense argument, cars are not devices crafted to kill as efficiently as possible, when cars kill, it is generally coincidental with their use.

        Yet! There is very little opposition to drivers being licenced, and much opposition to the users of the killing tools (firearms) being licenced.

    • Shandra,

      Way to hysterically flock to the first gun-related thing you see and make uninformed comments that do little more than dance on the still-fresh bodies of slain innocents to further your agenda.

      You’re a real class act, baby.

    • Why do you want to MURDER innocent babies in their mother’s womb and then sell their body parts to the highest bidder? Shandra you’re a mother, I ask you, why do you submit to ghoulish wanton murder?

  52. What are you doing to stop gun violence in the usa soil using AR15 assault weapons. Tell me if you can what are you doing. Assault weapons are intended for war combat but are used for mass shootings in the usa. Have you contacted the 4 decade lobbyist NRA Marion. P. Hammer who is the reason why we have gun massacres constantly. Do you care?????????

  53. Car ownership is not a Constitutional Right.
    The 2nd Ad. is there so that the Citizens can own Military Weapons to defend the Country from Tyranny, both external, such as when the British invaded in 1812 & burned the White House & especially Domestic Tyranny like we have now as we make our decent into what is clearly a nascent Police State.
    The 2nd Ad. was never intended as a Right to own Hunting & Sporting Weapons, as that was a given at the time the Bill of Rights was Drafted. The British confiscated ALL Military Weapons when they sent their Redcoats to oppress the Colonists.
    With any substantially sized Freedom as huge as the 2nd Ad. you will have People that will certainly abuse those Freedoms & cause collateral damage.

    • You suddenly awake in low light and realize you are confronted with a man’s coarse voice. There is a cold metal object pressed into your left temple. “Get up.” You ponder – “Who is this?” It is dark. You are assaulted with a litany of aromas of alcohol, marijuana…foul smelling breath…and body odor. This is real. You are plank walked to the dark hallway outside your bedroom where you gather your thoughts. He’s revealed that he and his cohorts have your wife and child at the barrel of a gun. As they duct tape your hands and feet, you begin to contemplate your fate and your family’s. A wave of fear comes over you because you realize your only weapon to defend yourself, an AR15, was confiscated by leftwing activists in your government after they instituted an illegal statewide gun-grabbing program. You were denied your legal right to arm yourself with a handgun because the state you live in makes it impossible to obtain a firearm for self protection. Your state requires a “need” that is determined not by the constitution or the citizen, but by the Sheriff who is a a known proponent of weapons confiscation and who stumped for your state’s Liberal, anti-second amendment governor.

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  55. How does the super lightweight barrel affect accuracy while firing multiple rounds? It’s always been my belief that a heavier barrel will maintain its accuracy better than a lightweight barrel.

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