Sig MDX Muzzle Brake ATF bout

Sig Sauer submitted its new Muzzle Brake to ATF for approval last year. Hoping they would receive a ruling similar to the recent news on their Sig Arm Brace. Unfortunately ATF has deemed it a suppressor and requires a Form 1 or 4. Sig intends on fighting this. I wish them all the luck.
Mac over at The Bangswitch has more information regarding this.


Nicholas C

Co-Founder of KRISSTALK forums, an owner’s support group and all things KRISS Vector related. Nick found his passion through competitive shooting while living in NY. He participates in USPSA and 3Gun. He loves all things that shoots and flashlights. Really really bright flashlights.

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  • Anonymoose

    I wish they had just put a full 16″ barrel on it instead of this crap. It’s ugly and pointless.

    • Blake

      If the ATF has their way, that’s a likely outcome…

      • Anonymoose

        I’d actually be okay with it if that was the outcome. However, I think the ATF probably will try to make them stop making them entirely.

        • Mickey R

          Seeing as how the MPX is being made overseas, ATF can’t stop them from making jack.

          • Anonymoose

            They can, however, restrict imports. =.=

          • Mickey R

            Indeed they can.

    • Cymond

      Well, it does have a point for anyone who wants to suppress it without also making it a SBR or making it even longer. And it’s not like a 9mm really benefits much from a longer barrel.

      If Sig’s appeals fail, they should also consider making a shrouded barrel like the Tactical Solutions SBX.

  • dan citizen

    what were they smoking that made them think that BATFE would allow a monocore suppressor without a can to be sold without an NFA stamp?

    What part of “readily converted into a sound suppressor” did they not understand?

    There are really only 3 possibilities here:
    1 – They are trolling BATFE
    2 – Their R-n-D and legal departments are completely unaware of firearms law
    3 – This is some ill planned publicity stunt

    • I remember seeing that at SHOT 2013 and thinking “boy, that looks an awful lot like a can without the can.”

    • Kosme

      “Their R-n-D and legal departments are completely unaware of firearms law”

      Well, they did get aproval for the “armbrace” wich is basicaly a stock with a hole in it.

    • erwos

      4. They read the law, and noted that nothing in it actually bans what they did. Quote the law. You’ll be surprised at what it actually says.

      • dan citizen

        I’m very familiar with the laws and this is so far over the line it can’t even see the gray area.

        Remember, possession of 1 K baffle constitutes a suppressor.

        • Only if that baffle is _only_ useful in a silencer. Otherwise, metal washers, metal tubing, small screws, rubber disks, etc. would automatically be “silencers” regardless of context.
          Since Sig can demonstrate that this thing is louder, AND provides recoil and muzzle control, ATF will lose.
          ANY muzzle brake with a medium or large expansion chamber can be converted to a silencer by sleeving it — it only takes 1dB of sound reduction to qualify under the law. (Which is why the old XM177 carbines were ruled to have “silencers” – the muzzle device intended to increase dwell time for reliability had a nearly insiginificant – but measureable – effect in reducing the sound.)

          • dan citizen

            In fact possession of unmodified household items have in the past been ruled to constitute a suppressor when constructive intent was determined to be present.

            This “muzzle brake” is the monocore of an already existent suppressor. It was a suppressor first and a “muzzle brake” second. it’s patent refers to it as a “sound suppressing baffle assembly”

            BATFE does not “win” or “lose” with these issues, this is an interpretation of existing law. They gave a decision and therefore will not allow issuance of an import permit without each example being an NFA item. They will not change their position on this one because it is a clear violation. Sig will not challenge the ruling because they have no basis to do so.

          • Um, SIg has already announced they ARE fighting it, and the basis on which they are fighting it.
            In fact, they had already filed suit on April 7th.

  • therapist

    So ATF has regulatory authority to determine what does or doesn’t constitute a silencer. Nobody is denying that. However, let’s pretend they don’t exist for a moment and consider this snippet of relevant U.S. code:

    ‘The terms “firearm silencer” and “firearm muffler” mean any device for silencing, muffling, or diminishing the report of a portable firearm, including any combination of parts, designed or redesigned, and intended for use in assembling or fabricating a firearm silencer or firearm muffler, and any part intended only for use in such assembly or fabrication.’

    Let’s list all the things that can be a silencer:

    1) Any device for diminishing the report of a portable firearm
    2) Any combination of parts intended for use in making a silencer
    3) Any part intended only for use in making a silencer

    Does the MPX muzzle brake meet the definition?

    1) Scientifically tested to NOT diminish the report. In fact, it enhances the report.
    2) Intended intended intended. This the golden word. Intended is the same word that landed the arm brace outside of title II territory. The arm brace is intended to be used as an arm brace for firing a pistol one handed. The MPX muzzle brake is intended to be used as a muzzle brake because Sig says so, they designed it, and it accomplishes exactly what a muzzle brake does and is scientifically proven not diminish the report of a portable firearm.
    3) See 2.

    The MPX muzzle brake, therefore, fails to meet the legal definition of a silencer. Let’s just hope the judge sees it that way too.

    • Mr Mxyzptlk

      I’d disagree with the 2nd part, if Sig had not intended the muzzle brake to be used for making a silencer it would not be threaded for the can at the front. They have even, rather naively, stated that this is one of the featured of the gun, so it is definitely INTENDED to be very easily turned into a suppressor.

      If they made the gun without the overtly threaded section at the front and didn’t tout it as being able to be suppressed, then they may have gotten away with it. As it is though even if they removes the threading now I doubt it would be approved, as putting a bit of round sleeving of some sort around the outside of the brake is too easy. Either they would need to give it a full length barrel, or change the profile of the “muzzle brake” (such as making it a twisted polygon or something) that would at least complicate the process of turning it into a suppressor.

      • Cymond

        I was just thinking about reprofiling the outer diameter of the brake, too. It would be easy to flute the brake so that it would require an internally fluted tube to function as a suppressor.

      • therapist

        Threading at the far end of the muzzle brake does not make it intended for use in making a silencer. A thread pitch can accommodate a wide variety of non-silencer parts, like a bayonet or flashlight mount.

        • Mr Mxyzptlk

          Except for the fact that Sig stated it was to accept a suppressor tube and have not come up with any other legit reason or accessory for it. As you originally stated it is defined as a suppressor if “Any combination of parts intended for use in making a silence” and as soon as Sig stated that this was one of the intended uses for the muzzle brake in combination with the threading at the front, they pretty much just shot themselves in the foot. Also, I’d dispute the idea that a large thread like this mounted on the front of a brake would be any good for mounting a bayonet or a flashlight, as it seems like an all around bad idea.

          • So, when threaded pistol barrels are sold (specifically designed to take suppressors, like every Walther P22 sold), does that make that barrel a “silencer part”? Nope. Which is why I didn;t have to file a Form 4 and wait 6 months to buy my Walther P22 — I filled out a 4473, swiped my card, and took it home.

        • raz-0

          Perhaps the fact that sig said they plan to offer a silencer add on that is available if you get the stamp would indeed imply ot me tha it is there to be converted into a silencer.

          However it is A part. Point 2 says a combination of parts, which by my understanding of the English language requires at least 2 parts. Heck even by math reasoning I’m not sure you can have a combination of a single item. Functionally, I don’t see a huge difference between this and some brakes that act as the mount and first sacrificial baffle for the silencer that works with it. This just happens to have all the baffles integrated into a single unit. Or so we assume. The screw on shroud that turns it into a silencer might have more baffles.

        • SUPER 68 IS DOWN

          All of my AR’s have a threaded barrel that can accept a suppressor. That does NOT preclude BATFE involvement (Tax Stamp) They currently have flash suppressors but can be installed with a suppressor within minutes

      • erwos

        Key word here is “only”. As long as it was designed to function as a brake, too, they’re technically in the clear.

        Further, a single part is not “a combination of parts”.

    • ATF just lost a nearly identical court case, that would have been easier for them to win.
      1. Does not actually diminish the report of the firearm.
      2. Is not a COMBINATION of parts to assemble a silencer — without the sleeve, no silencer is possible, and the device still functions as a muzzle brake. (Otherwise any barrel threading would make a gun barrel a “silencer”).
      3. Between 1 & 2, it is apparant that this part is NOT “only for use” in making a silencer.
      ATF is going to lose this one, just as the lost they Vollmer case (which rejected the ATF’s “Once a machinegun, always a machinegun” interpretation), the T/C case (which rejected the ATF’s “constructive possession” interpretation about having a handgun frame, short barrel, long barrel AND stock all at onc), and even an earlier case involving a felon in possession of a flimsy “gun” (being sold as a coyote extermination trap, and intended to use a primer to shoot a poison pill down a coyote’s mouth when it bit the bait – the felon was cleared to work as a coyote extermination specialist after release from prison) so shoddy the ATF examiner was afraid to fire a live round through it (the court, Warren Burger himself, said, if any reasonable person can figure out – like an ATF examiner – that it WILL blow up when fired with real ammo, it isn’t a “firearm” for teh purposes of possession.)

  • guest

    This is NOT a brake and Sig knows it.

    • Jeff

      Maybe but neither is it a suppressor.
      I can’t believe manufacturers are required to apply to ATF to begin with.

    • Sez Eye

      An unsupported opinion. Since it reduces muzzle lift and recoil, it is indeed a brake, regardless of its appearance or construction. It certainly isn’t a suppressor.

      • guest

        If one shoves a tube of fitting diameter arund it and it’s a suppressor. Hence the ATF conclusion of “readily convertible”. This is about as readily as it can ever get.

        The ATF is actually doing all the wannabee-specops a favor here by not allowing something that could easely land each “ethusiastic innovator” behind bars in a fed jail for “experimenting” too much with that “brake” without having applied for a can.

        • Sez Eye

          Do you not realize that you just supported my position. Without additional parts it is simply a muzzle brake. Using your logic, the pipes in my house are a bomb because they are “readily convertible” with the addition of a few parts. Indeed, I have several guns that have threads on the end, Are these also to be called a silencer because they are “readily convertible” to a silenced configuration?

          • guest

            You have bewildered yourself in your own irrelevant comparison.
            A threaded muzzle can never become a silencer, it is not a “configuration” that is a taxed part but the device itself.

            Here sig basically made a baffle stack, and claimed it to be a “muzzle brake”. Tell me, have you ever seen such a “brake” anywhere else, with baffles angled down? This would otherwise causes muzzle rise, which I don’t believe has been practiced by any manufacturer, ever. Look also how it extends into the handguard. Do you really believe venting hot gases INTO the hand guard is a good idea?
            This is basically the gun world’s answer to a beer can in a paper bag. “well you don’t know if I am drinking in public, hurt durr durr, legal sass!”

            Do yourself and everyone else a big favor: these “arm braces” and this “muzzle brake” paired with their very questionable legal status may land people in federal recreation facilities for many years. You want an SBR with a can – great. Apply for it and be done with it.

          • therapist

            “Tell me, have you ever seen such a ‘brake’ anywhere else, with baffles angled down?”

            It’s called the EFFIN-A compensator. The ATF would hire you as an attorney for this lawsuit, because Sig’s lawyers would wipe the floor with you.

          • Guest

            A compensator that will release hot gases into the handguard, at a downward angle while bearing a 100% resemblance to a baffle stack? Your temper does not provide a good counter-argument for neither of these properties.

            Time (or trial) will tell. I hope to see you around in the comment field when that happens, when you will have to eat your own words about anybody being wiped.

          • Well, Sig has something better than eyeball guesstimates. They have lab test data to back their claim it functions as a muzzle brake.
            NOTE — they never claimed it was a GREAT brake, nor does the law require that. You are still allowed to make inefficient products.

          • PPSh41

          • bull

            no not forget the evil pillows!

        • “Readily convertable”, however, DOES NOT APPLY TO SILENCERS.
          Silencers have a statutory definition.

  • matt RRC

    I’d rather see them fight something like the 7n6 ban. I saw this at SHOT and they show it as a muzzle brake and then “if you pay the stamp (guy slides can on) you have a suppressor!” I am glad they are fighting the ATF anyway but this seems like an ill advised battle.

    • Anonymoose Supposedly they have easily changed barrels in the new xi rifles. Maybe if they had a 5.45 version of the xi Russian they would be inclined to do just that, or possibly manufacture cheap 5.45 through their new ammo department.

    • Nolan

      As far as I can tell Sig doesn’t have anything to do with the 7n6 ban… They (as far as I know) don’t sell anything chambered in it… Why would they spend their time and resources on that?

  • Laserbait

    That has got to be the worst design for a brake. With all of the baffles/chambers pointing like that, it’s going to force the barrel up with every shot.

    C’mon Sig, at least try and make it plausible that is a brake before schlepping it off to the ATF…

    • They have test data to back their claims that it works as a muzzle brake.

  • Dan-O

    Don’t confuse the legalese used to legitimize the SB15 with their attempt at the MPX “brake”. There is no gray area to speak of, as the law prohibits any device that can be “readily” converted within reason:
    ar15 barrel with a muzzle thread; it can accept a suppressor but does not make the AR the discriminate object, the suppressor is.
    The MPX with the goofy baffle/brake system: because it is an inherent feature of the system itself, the system becomes the discriminate object. Since Sig proved it can be easily converted with a threaded shroud to used as a suppressor, it becomes an inherently easy to make/mod suppression device regardless of what its intentions were without the add-on shroud.
    I don’t admire or work for the BATF, but the law is what it is.

    • Dan-O: please cite the part of the statute that includes “readily converted” in relation to _silencers_. ATF uses “readily converted” as a synonym for “readily restored” in regards to machineguns, but then the statutory definition of “machinegun” includes things that are “readily restored”. Silencers use a different definition.
      (Historical reason _why_ the discrepency — people were field stripping machineguns and claiming they weren’t machineguns, because they didn’t work at that time. Heck, a government-approved DEWAT for a MAxim MG08 was simply “break the feed pawl”! The GCA amendments to the NFA specifically altered the definition of “machinegun” to include both stripped receivers and guns that could be restored and made functional rather easily. No such problem existed with silencers.)

      • Dan-O

        It’s getting into semantics then. The BATF’s main argument is it can still be easily manufactured into a suppressor. The baffles are a key ingredient to any suppressor recipe, and the fact it’s a pre-manufactured part of the gun is what got their panties all twisted.
        Kudos on the historical fact btw 🙂

  • echelon

    Sig and everyone else is going about this all wrong…

    Solution: Abolish ATF and end GCA/NFA “laws”.

    Let’s try something novel: If you kill or maim someone with a gun, not in self defense, then you get the book thrown at you. None of this reduced sentence junk or whatever. I don’t care if the gun is full, semi, loud or quiet…if the human uses the tool to commit murder then bad things should happen to the offender.

    Besides, if anyone really wanted to make a suppressor they can easily out of household items and they could care less about what the ATF or anyone else says…

    And the argument about “dumb criminals” doesn’t apply in the internet age. Youtube has step by step instructions or you can simply buy a thread adapter off Amazon and an oil filter from wal mart…doesn’t get easier than that.

  • gunslinger

    why does it have a thead on the end? i don’t get it. i can see how it would be relatively easy to get a tube to screw on to this, then have a cap on the other end that screws on, but leaving room for the thread attachment to the barrel, thus making a full “can”

    this is compared to taking a pipe, making your own baffles, making sure they are in alignment, etc. much easier here, imho.

    i can see why the ATF said what they did.

  • BR549

    Yes, but all this thing needs is a sleeve to fit over the device to be a silencer. The device, by itself is just all the guts of a silencer molded into one piece.

    I think it looks kinda sexy, myself, and of course, the ATF has no business meddling in state issues, but I have to say that this one is “busted”. Nice try though.