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It all started with the Honey Badger, a strange yet awesome creation from the R&D department of Advanced Armament Corp. back in the day. The plan was to create a do-it-all weapon, one that’s shorter and quieter than an MP5, has the barrier penetration and “stopping power” of an AK-47, uses as many standard AR-15 parts as possible, and can swap from subsonic to supersonic ammunition without needing to adjust any settings on the gun. That’s how the 300 AAC Blackout cartridge came to be, and now SIG SAUER is in the process of perfecting the rifle even further. Enter their MCX . . .

The basic concept hasn’t changed — it’s still a rifle designed to take full advantage of the 300 AAC Blackout cartridge. The gun functions flawlessly with both supersonic and subsonic ammunition, swapping between the two without needing to change a single setting on the gun. But SIG has made some interesting design changes since the original Honey Badger debut that have some impressive effects on the size and function of the gun.


The biggest change is that the gas system has been swapped to a as-yet undisclosed short stroke piston based system instead of the standard AR-15 gas expansion system. The original spec for the rifle required the Stoner designed system to be in tact, which explained the short receiver extension that was an integral part of the Honey Badger design. Since the need for a buffer tube is gone, so is the receiver extension in SIG’s design. Instead they opted for a Picatinny attachment point like that on the MPX, allowing the end user to put whatever kind of stock they want on the gun. There are also two QD cups machined into the lower receiver for sling attachment points, should the user want one.


The second big change is the silencer. Ethan Lessard was the R&D guy who spearheaded the original Honey Badger and AAC’s other silencer designs, and for the last two years he’s been working with SIG on their new silencer designs. The latest iteration is so new that when Ethan brought it out to the range it wasn’t even painted yet. Apparently they’ve found a way to remove the spacers in the silencers which were an integral part of AAC’s design and simply weld one baffle straight to the next in the stack. This, combined with some other design improvements, have knocked another 10 dB off the sound meter compared to the original Honey Badger design.

The last real improvement is the forend of the rifle. With the Honey Badger, it was fixed in place. But with the MCX, the lower portion of the handguard can be removed by simply taking out two screws at the rear of the barrel. There’s no need for specialized tools or fiddling with the barrel nut, it just slides off easily and quickly. The current version of the gun uses a carbon fiber forend with some holes drilled for rail sections, but the R&D guys say that they’re probably leaning toward a keymod version for the final product.

The rifle just feels…right. Even with the can on the end, the gun balances well and is very easy to keep on target. The controls are crisp and clean, and the gun is really just a pleasure to fire.

While the gun may look finished, there are still one or two bugs to work out, like the one I captured in the video above. The 300 AAC Blackout cartridge is designed to completely burn its powder charge in nine inches of barrel length, so when you have a rifle with a shorter barrel (like the Honey Badger or the MCX) there’s some unburnt powder left that gets dumped out the front. Add a silencer into the mix and all that unburnt powder starts accumulating in the first baffle chamber. When the conditions are just right, the powder may ignite and the back pressure from the silencer will blow the flames out the chamber and ejection port.

Kevin says it’s rare, and they’re working on fixing that issue. I said the better option would be adding chrome exhaust pipes to the side of the can and maxing out the powder charge.


The rifle isn’t quite finished, but even as-is, it kicks ass. The current scuttlebutt is that SIG will be releasing both a 16″ version of the gun as well as a pistol version with their pistol arm brace (a stamp-free SBR basically), but no matter which version you get changing barrel lengths will be easy as pie. The gun is designed to be a true multi-caliber firearm, with barrel changes being an operator level action. The gun will be first available in 300 BLK, with rumors for a 7.62×39 and 5.56 NATO conversion kit coming down the line, and if you want a different barrel length then you can change that on the fly as well.

It really does look like SIG Sauer took the concept of the Honey Badger and ran with it all the way to the finish line. And then decided to make it available for sale to the civilian market and not just for military contracts.

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  1. Neat. Keep the cost below the scar platform and it’s a winner. I assume it’s something similar to a sig556 design but perhaps lightened in key places. I’ll watch the vid when I get home. Fairly interested in this and the mpx.

    I wonder if it’s quieter than the Liberty Leonidas….perhaps some independent testing is in order. Sig, lemme know. I can put you in touch with some folks.

    • The thing could be more expensive than the SCAR platform and still be a winner, you don’t exactly set the bar high with the SCAR.

  2. So, would it be said that Sig’s recent products would be an improvement over the last? I know for a while they had a bad reputation and I’ve avoided products because of that, however the 556XI appeared here and it looks mighty nice.

  3. This is something I would actually purchase without any hesitation. You really have to give a hand to SIG for all of the awesome new offerings available for civy purchase. Like the Sig Sauer P716-PSB Pistol. I really hope the ATF lawsuit goes well for the MPX. But that’s a whole new story in itself.

    Glad to see the Honey Badger went somewhere, and hope to see this on the shelf soon.

  4. No pics of the action? I’d love to see what they did to get rid of the buffer tube. I imagine the piston system is similar to the 516.

  5. OK Nick, the one thing I’ve been thinking about 300BLK in subsonic lately is, how much better is it, inside 50 feet, than a 45ACP? 45 = 200-230 grain bullet @ 850-950fps 300BLK 200-220 grain bullet @1000fps.

    Can we get @ShootingTheBull410 to do a side by side gel test?

    • Don’t forget that 300 BLK uses a spitzer bullet, retain velocity better and better penetration.

    • Well, if you know the speed and weight of the bullet, the energy of each can be figured out. Using the high numbers from your post for each bullet puts a 220 grain .300blk traveling at 1000fps at just slightly higher energy than the .45ACP 230 grain bullet traveling at 950fps. I would assume that the 300blk would see that difference get larger as the distance increases, but straight out of the barrel, they would be pretty similar. The biggest factor is the speed since it is squared and the weight of the bullet is halved in the formula.

  6. @seans I don’t think it can. If it were a nice precision rifle that was made to shoot quarters at 500yds? Yeah. A suppressed carbine that isn’t a precison rifle and will spend most of its time doing $.40 a round mag dumps to impress friends and pretend to be doing over the beach testing? No.

    Again, i don’t drink the cool aid of 300BLK and don’t believe it’s the end all be all cartridge before we get to phased plasma rifles. I think it has a long way to go.

    • Have you seen what a suppressed blackout can do out of a shorty, its impressive, guys have had kills past 600 yards out of short barrels with it. Also have you actual experience with the SCAR platform. I have, had to be a assistant ordance rep in charge of a platoon worth of the things, have seen other platoons write ups of them from deployments, they are a piece of crap. Unfortunately there is nothing else around battle rifle wise for the majority of SOF unless you are in SMU, then you got the HK417.

      • in order of question.

        yes, i have experience with 300BLK. i remember the day it was announced on silencertalk. you can to go the thread on silencertalk and see my response.

        Yes, i have some (limited) experience with the scar platform. i got to shoot nick’s scar at a range when meeting him for a firearm he wanted to test. id say nick was happy with that gun and he fired quite a few rounds through it. i would not call it a piece of crap. expensive and perhaps not completely thought out? yes. inordinately complicated for an infantry-level rifle? yes. crap? surely not.

        SMUs can have most anything they want, not just the 417….

        • So your experience with the SCAR is limited to a range day, mine is years. Including combat deployments. As I said, I was a ordance rep, read the other reps reports, they have a extremely high malfunction and breakage rate. Far to high for any combat rifle. Having to have up to 25% of your rifles replaced on deployment is not acceptable. Your right the SMUs can pretty much use any gun they want. And they don’t use SCARs, that should tell you enough about the rifle. They also use .300s. 300 at this point is a battle proven round. It gives the operator MP5SD level sound reduction with a rifle caliber round. Also while still allowing them standard engagement distances with supersonic rounds. Its nice not having to lug around both a rifle and a MP5SD to stay quiet.

    • I’m not aware of any rifle caliber that cycles in the subsonic / supersonic manner out of an AR style platform other than the 300 AAC. While there are loads that can certainly cycle subsonic / supersonic from a semi auto pistol or rifle – hey 9mm. .40, .45 ACP – the energy and barrier penetration capabilities do no significantly change. The subsonic pistol rounds will be in the 300-500 FPE range, and the supersonic version will be 400-600 FPE or so from a pistol cal carbine. The 300 AAC can hit the same subsonic energy range with supersonic loads well over 1000 FPE. In so doing, the 300 can penetrate IIIA vests, and can travel with a 400-600 yard effective range or more.

      The 5.56, 6.5, and 6.8 cannot cycle sub sonic without modifications. All the 300 needs is a mag swap. The 7.62 x 39 can do some subsonic / supersonic cycling but requires a lot of curvature to the magazines.

  7. If it can work as advertised, this is an A-plus. The versatility of the 300 AAC cartridge allows good subsonic accuracy, power and stealth. The supersonic rounds will defeat typical battlefield barriers better than a 5.56. A 400-600 yard effective range in a weapon of similar size as the pistol carbine – which quickly runs out of energy and carriers significantly less barrier penetration potential.

    Spec Ops will be snapping these things up. Kudos also to Sig for making this available to us uniformed and non uniformed civilians. If I didn’t live in Commiefornia, I would be buying this in a heartbeat – plus the epic NFA wait period. Should I even ask a dumb question if they will make a version available for us Californians?

  8. I hope I’m not the first to notice that Nick never let off the go pedal when FIRE WAS INCHES FROM HIS FACE.

    • It was only for a split second, facing away from him, so I doubt he much realized it untill afterward. And he said he wanted the designer to do up some max load and add exhaust ports to the suppressor.

  9. You remember the old Warner Brothers cartoons from the 40s when a wolf would see a pretty woman walk by, and his eyes would bug out and his jaw would hit the floor? Great looking weapon. I didn’t realize I needed one until I read this column…

  10. I am sticking to short-barreled AKs. Easier that way. Ain’t drinking the 300 BLK kool-aid mainly because I have been enjoying something much older that is pretty much the same. I will admit it is really funny to me how the Russians were/are way ahead of you, yet you still call Russians stupid and backwards. Stuff like the:

    -DMR concept & DMR rifles
    -IAR (AKA assault rifle with heavier barrel and bigger mags)
    -7.62×39 ballistics (AKA stubby, short cartridge with a case that isn’t much wider than the bullet)
    -Piston driven rifles (I know Russians didn’t invent them but they used them way before they became all the rage)

    Regarding the fire-breathing suppressor, what about using a 9 inch barrel since that is what the cartridge was made for?

    What is the db reading? Since you said that they knocked 10 db off it would mean that either the starting point was bad (in the 20 db range) or that they have something amazing (40 db reduction) in the true sense of the word.

    Regarding long-range performance:

    People use 300 BLK at 600 meters, but if I suggest doing the same with 7.62×39 people say it is impossible/a lie and the like (hint: it is possible, don’t use shitty ammo and have a good barrel).

    • As a guy who is no fan of Russian firearms, and believe there are some things they do well, and some they don’t. I feel the Russians have been decades ahead in some weapons development, but they have failed to modernize and implement their weapons as the west.

      • True that.

        Always a good/bad side to it. Russians are good at making things but they also haven’t modernized their things. Simple things would be nice, like a collapsing AK stock with adjustable cheek piece. Or peep sights on the AKs and Dragunovs (stuff like Tech-Sights or the Finnish AK sights come to mind).

        In my opinion they made a mistake by switching to 5.45. There has to be a reason for stuff like 300 BLK or the fact that other countries still use 7.62×39 AKs.

        • Russia never really abandoned 7.62×39 – it’s still in heavy use by interior & police forces, and still common to find a PBS suppressor-equipped AKM in many squads, as 7.62×39 works just as well as .300 Blk with a suppressor when used with subsonic ammo. Subsonic ammo in 5.45 basically does not exist.

  11. Thanks for the review. What type of folding stock is that in the picture? Available aftermarket or Sig proprietary?

  12. You say silencer more than 3 times in this report. I know it’s nitpicking but it should be supressor not silencer just like it should be magazine and not clip.

    This would be a nice platform but what is it going to cost and will there be a non supressed version so I could buy without that stupid NFA registration?

    • it doesnt matter what you call it. atf on a form 1, 3, 4 etc call it silencer. there is no “suppressor” box you check. please dont get all wound up about it. we all know what it actually does (And those that dont i urge you to find out).

      im expecting $2500 in my non-scientific/the-mpx-is-$2000-without-a-can-on-it price analysis and projections.

    • Legislature calls it “silencer”

      Its creator (Sir Hiram Maxim) also called it a “silencer”

      In short; deal with it. A biy funny is that it is called a sound-dampener in many European countries.

    • I used to think that also but I was wrong as they were first called silencers when they appeared on the scene many years ago. At that time they did not know what a suppressor was.

      The newer term “suppressor” does describe what they actually do.

  13. With Kevin over at Sig now, their NFA lineup is building momentum and looking really good!

    As I said about the MPX, too bad we can’t have private ownership of the full auto models.

  14. The MCX featured in the video above is 120dB. That’s 10dB quieter than the MP5-SD, and as quiet as the new SF Ryder .22 silencer.

  15. Last I heard AAC’s Honey Badger wasn’t dead, nor was it to be restricted sales only.

  16. 120db you say? Was that mil-standard testing? Calibrated meters? What ammo?

    Sorry to poke holes, we just have a standard way of doing things.


  17. Hey Nick, always lucky to test new gun !
    I wonder if this gun is not “overgasported” ? Got the impression of a russian MG. The brass is kicked like hell and is bulged after it has been ejected. Plus the big fireball at the ejection port, impressive !
    What do you think about that ?

  18. This is great. A PDW in 9 inch barrel,.300 Blackout cartridge, Brace Legal, New ATF Rule Interpretation; intent, design, Fxn crap. Just cannot shoulder it and does not contain me under the NFA
    How does it compare to PTR 51F:.308 cartridge 8.5 Barrel. Generalized info, can I pick somebody’s brain, ( real gunners out in the field)
    .308 needs a long barrel for powder to fully burn produce the velocity that is its fame and purpose.
    A 8.5 Barrel leaves unhurt powder and supposedly lose 400 ft/s velocity( somebody said)
    Would a faster-burning powder maintain.308’s range.
    PTR 51F, PTR X3P ( same.308 but handgun Rd has rails, uses the Brace too.
    If.300 Blackout is as potent as said, I think I will wait for the SIG.

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