Sig Sauer vs. ATF on Pause Pending Third Muzzle Brake Classification

SeaCoastOnline has reported that the lawsuit between the Sig Sauer and the BATFE is now suspended pending the ATF’s reevaluation of the MPX muzzle brake. The suspension is mutually agreed upon by both the ATF and Sig until the ATF concludes a formal third evaluation of the device due August 6th. If the ATF rules against the device again, the lawsuit will resume.


The Sig MPX model in question with the extended muzzle brake.

Sig Sauer had originally filed suit against the ATF alleging after a ruling that the civilian-legal MPX-C with an extended muzzle brake was considered a “silencer” and thus subject all applicable NFA regulations. Sig disagreed with this assessment claiming:

…it designed the muzzle brake which “effectively reduces recoil and muzzle rise when a shot is discharged” and as such, it’s not subject to regulation under the federal Gun Control Act.

“Accordingly, it will be highly marketable to consumers and will generate profit,” according to the suit.

If classified as a silencer or muffler, “no market would exist for the device,” because consumers would not subject themselves to the “required burdens” associated with silencers, to buy a device that doesn’t perform as a silencer, Sig claims.

The ATF originally asserted that the brake was designed solely to serve as a “monolithic baffle stack” suppressor. The fact that it was welded to the barrel made no difference. The ATF stuck to its original determination after a follow-up letter from September 2013 in which Sig produced evidence that the brake did not suppress sound (in fact, it amplified it) and did reduce recoil to the shooter.


My take?  With the recent decision on the “arm brace” Sig is going for broke. Assuming they brake cannot be “easily converted” to a suppressor (which it does bear an uncanny resemblance to a can), Sig will likely win. If it goes to trial, it will be beneficial for the industry to understand what criteria the ATF uses to determine a “silencer”. If they do not have guidelines, this will force the ATF to create them, likely allowing similar devices to the MPX-C.

That said, from a financial aspect, this suit is almost moot. Sig will likely sell significantly more of the arm brace versions than the MPS than the “C”, which will be popular only in restricted locales.

Cover photo courtesy of and Invictus Tactical Review. 

Nathan S

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

The above post is my opinion and does not reflect the views of any company or organization.


  • Mr Mxyzptlk

    Ignoring the legal question for a minute, am I missing something or are the baffles the wrong way up to prevent muzzle climb? It seems like they would direct the gas downwards making the muzzle rise worse wouldn’t it?

    Legal wise, I think Sig have pushed this too far, as it seems like that is way too easy to convert to a suppressor. Hell, I’d be curious to see a test where somebody just wrapped a roll or two of duct-tape around that “muzzle brake” and see what happens (having done some pretty crazy stuff with duct tape I imagine it would actually last pretty well). Also, if it was just a muzzle brake that happened to be this shape, then so be it, but the fact that Sig have built the threaded section into the end and have stated that this muzzle brake was specifically designed this way to act as part of a suppressor really doesn’t help their case.

    • N4choLibre

      But the question is how effective would your suggested “duct tape suppressor” be in muffling the sound? And with no guidelines in place, how does the ATF justify what constitutes a “suppressor” if the duct tape suppressor only muffles the sound by a few db? The argument could be made that you could easily produce a make shift suppressor and use that on a regular rifle with the same or better effect, so why is it justifiable for the Sig Saur to be banned, especially if the conversion in question only barely stifles the sound? Obviously this is based on how effective such a device (if you could constitute duct tape as a device) would be, subject to testing.

      • Mr Mxyzptlk

        The duct tape thing is just a crazy idea I had, but honestly, I imagine that it would be as effective as the actual can for a few shots at least.
        I think the thing that constitutes this as part of a suppressor, is the fact that it is, well, half of a suppressor. SIG has made no secret of the fact that they designed the muzzle brake to act as the coreof a suppressor, so I don’t understand why they ever thought they wouldn’ have a problem with the ATF about it.

        Forgetting the basic 50 cent tape idea, something that just needs a sleeve put over it is orders of magnitude closer to being a suppressor than a maglite or something like that. I know for a fact that I could turn that into an effective suppressor, but couldn’t build one from scratch.

        Even if something like this is technically not illegal (although by my reading of or the law I believe it is), i beliv that all that trying to introduce someone something like this will do is to lead to a change in the laws so aw o specifically exclude it.

        • Michael Bergeron

          I don’t know given that Oil Filters can be made into fairly effective silencers with a simple 1/2″ male to whatever and oilfilter threads to adapter shows that easy is a relative term

          • Mr Mxyzptlk

            If you were selling an adapter as a suppressor adapter, then it would be illegal on the same grounds. It is due to the fact that they are sold as “solvent trap adapters” or something similar that allow them to be technically legal (or at least a grey area). Even though they can be used to make suppressors (I would argue much less effective and evolved than the one that would be created by putting a sleeve over this brake though) and this was likely what the people making them wanted, this is not their official purpose for the part, as opposed to the Sig brake which is officially intended as a suppressor part.

        • Cymond

          “something that just needs a sleeve put over it is orders of magnitude closer to being a suppressor than a maglite or something like that”
          Ok, well as you suggested, an ordinary brake could be wrapped with a sleeve. It may not work well for .223, but I would bet that a multichamber brake would give decent suppression for a 22lr.
          “the fact that Sig have built the threaded section into the end”.
          Ok, yes, it is easy to convert the MPX brake, but it is still just a brake. Yes, it is intended to be convertible to a suppressor with a registered tube, but it is also intended to be a muzzle brake. It is a dual purpose device. Yes, it has threads on the end, but so does the Ares Armor Effin-A adjustable comp.
          Personally, I think it’s a genius idea. First, current integral centerfire suppressors are mostly produced as individual units by gunsmiths, not mass produced. Second, most integral suppressors weren’t even user-serviceable until a few years ago. Currently, we have designs like the Tac-Sol Sawtooth or Thomson Machine Operative integral suppressors. The tube is integrated into the barrel, and the monocore baffle stack pulls out the front. Of course, this gets into the silly issue that both the tube and core are considered suppressors (because they’re only useful as suppressor parts) so neither part can be sold unregistered. With Sig’s design, the brake/core is integral and dual purpose. As one possible use, an integrally suppressed MP-X could be taken across state lines (even into an anti-suppressor state) by simply removing the outer tube. You can’t do that with an Operative.

          • Mr Mxyzptlk

            Sig cannot have it both ways, either they make it a long multi chamber brake to get the barrel to 16″, or they have a barrel with an integrated suppressor core and sell it as a registered suppressor part. As the ATF make it necessary for the suppresor core to be registered, why do people think it would be any different when it is already attached to the front of a barrel? I know, I know, “It’s also a muzzle brake”, but there are features of this “brake” that mean it is specifically designed to act as part of a suppressor. If this sort of thing flies, then surely you should be able to buy the core of a suppressor as it has other uses, like working as a rather interesting looking cookie cutter, or a paper weight, maybe if it has shard edges on the baffles you could use it as a pencil sharpener. Similarly, the tube could technically be argued to have the secondary purpose of being a sleeve to hold a series of barrel weights or something

            Just to touch on the Effin-A brake for a second, the big difference between the two is, again, the intent with which they were designed. Firstly, the design of the Effin-A would be absolutely awful for a suppressor, and it was not built with this in mind, unlike the design of the Sig Brake. Secondly, the threading on the Effin-A is there for the purpose of stacking the compensators to increase it’s length or effect, as opposed to the Sig brake threading which is designed for use in converting it to a suppressor. MAYBE if Sig came up with a genuine use for this threading and had never mentioned the concept of this being designed with suppression in mind then it would be fine, but as they haven’t, and as it wasn’t, they are facing this problem.

            I feel I should probably clarify, I personally do not think that this should be illegal. However based on my interpretation of the current laws in the US, I feel that it will not pass muster with the ATF. This is clearly also the reading of the situation by some people in the ATF or the situation wouldn’t exist, and as it is the ATF that makes the decisions Sig might be shit out of luck in this case. Maybe with this third evaluation they will be lucky and somebody will see it differently, however I doubt this will be the case as if they allowed this then it would set a precedent, and could lead to other companies producing products that are just taking the piss.

        • Emir Parkreiner

          By your logic owning a rifle/shotgun and a hacksaw should constitute constructive intent of an unregistered SBR/SBS.

          • Mr Mxyzptlk

            No, I totally fail to see how that is relevant in any way to what I said. A comparable analogy would be if somebody sold a shotgun where the front end of the barrel threaded off and they said that “this is a take-down shotgun, but if registered as an AOW then it can have a shorter barrel”.

          • Emir Parkreiner

            You stated that you believed the sig brake to be unlawful due to the fact that the nature of its design facilitates construction of a suppressor (in this case through the use of duct tape).

            When applying that same logic (lawful intended use is second to potential unlawful abuse) to rifles/shotguns, one could claim that they should be illegal due to the fact that they could quickly and readily be converted to an illegal SBS/SBR with nothing more than a simply hacksaw.

          • Mr Mxyzptlk

            Firstly, I didn’t say that duct tape was the way to turn this into a real suppressor, all I said was that i would be curious to see how well it would work as it is potentially a somewhat effective yet incredibly low tech way of doing it. Obviously putting some kind of metal sleeve over it would be the way of doing it properly, but even this would be easy to either make yourself, or to buy something off the shelf of a suitable size (for example I know there is a place down the road from me that sells stainless steel tubing in 1 or 2 mm diameter increments which would be perfect for the job and only cost about $10-20).

            As to your main point, you seem to be totally ignoring the fact that Sig has built this brake INTENDING it to be used as a suppressor component. When somebody builds a shotgun, they are not INTENDING for you to take a hacksaw to it to shorten it. If you honestly still cannot see the difference between these two situations, then so be it.

          • Emir Parkreiner

            Sig has made it abundantly clear that the PRIMARY intent of this muzzle brake is simply that, a muzzle brake. The fact that it can be used as a suppressor component is incidental.

            Suppressors and suppressor parts are both regulated as Title 2 firearms. Theoretically, the flash hider that most QD suppressors use as a mount should also fall under title 2 as it is a critically important component of the silencer and absolutely necessary in order for the silencer to function.
            However, this is not the case. Why? Because their first and foremost intent is to be used as a flash hider. The fact that they can be as a suppressor component is immaterial as it does not invalidate the primary intent.

          • Mr Mxyzptlk

            This brake is a suppressor component, surely that is not in dispute. Sig have said this is the case, and surely any rational person would agree. A flash hider with a QD mount is not a suppressor component, it is purely used to attach a specific type of suppressor.

            Having a QD suppressor does not help in any way in making a DIY ghetto suppressor, and in and of itself it provides no suppression level, and on the finished suppressor it is not a component of the suppressive function and is purely an attachment method.

          • gunslinger

            see the video above by wetcorps. Sig intends the device to become a silencer. although they did mention that you need the tube and paperork, but they intended this as a component that can be converted to a can.

            i think that hurts them. if you look at the arm brace, they never said (in anything i saw) that they intended you to fire from the shoulder. it was ONLY to be used with the straps to attach to the forearm to assist in aiming.

            i mean, this is how i’d argue if i was the lawyer.

    • BOB

      but what is the definition of ‘too easy’? Is a maglite ‘too easy’? Is an oil filter, ‘too easy’. Using undefined terms like ‘too easy’ is never helpful.

    • Daisuke0222

      I don’t intend to argue the legality of this thing one way or the other, but from a philosophical POV, I’m not sure I understand why “silencers” are the subject of so much sturm und drang on the part of the ATF and gov’t agencies in general. It seems to me that quieter is better, though I suppose a maniac with a suppressed weapon in a crowd could possibly do more damage before the unarmed masses would understand the need to run away, and shootings from long-range sniping (for lack of a different term) would be harder to track down. I wonder, though, how much objective data exist to show that suppressors need to be “suppressed” with ATF tax stamps and so on, as a bulwark against illicit use? Precious little, I’d imagine.

  • wetcorps

    I’ll just leave this here…

    I love how he manage to be all inocent and keep a straight face all along 😀

    • J.T.

      Yep. SIG was advertising that it was essentially a baffle stack and that it was easily converted into a silencer. It was a primary selling point of the gun. If the ATF doesn’t change their mind and it does go to trial, I don’t see SIG winning. The design is dependent on barrel length but it shouldn’t be too hard to re-design without the threads on the end and that would kill the ATF argument..

  • Anonymoose

    I dunno man, if you told me I could get 9mm carbine with an integral suppressor (assuming it actually was a suppressor and not 10″ of goofy “muzzle brake” crap) I’d jump right on that.

    • Annika R

      I agree, although a lot of it is going to depend on the pricing for me. If the MPX-C costs more than your average alternative 9mm pistol+arm brace+detachable silencer then it would not make financial sense. What I’m hoping is that the carbine with whatever silencer-creating tube is offered together will end up costing less overall.

      • wetcorps

        He says about 2200$ in the video.

  • Nicks87

    Fight the power sig!

  • erwos

    IMHO, this sounds VERY good for Sig, forgive the pun. The BATFE wouldn’t bother with this new opinion crap if they were just going to reissue the old one – I rather think most judges would be pissed off if they pulled a stunt like that.

    If Sig wins, this concept of perma-attached baffles/comp/brake could have a massive impact on the entire industry. You’d be getting SBR-length guns with user-serviceable suppressors on a single stamp. You can do that now, of course, but good luck with warranty service.

    • JumpIf NotZero

      Might larger concern is that some mentally ill lunatic goes into a shop, buys an MPX-C, goes and secures a tube to it, then shoots up a mall.

      In one single swoop you get calls for silencers to be illegal, a reversal on brakes that “could” be silencers, calls for an AWB and magazine limits again.

      It’s just pushing the stance on readily-convertible stance a tiny bit too far too quickly imo.

      • wetcorps

        Well you won’t kill more people in a mall with a silencer on… And at least the survivors won’t get earing damage.
        Be a respectful mass shooter, use a silencer!

        • JumpIf NotZero

          Oh I fully agree. Shooting suppressed is the polite thing to do.

      • Danmaku

        Because if we act more considerate of the OPFOR’s talking points, they surely will stop trying to take our firearms. Sure, you go for that.

      • BryanS

        They are more likely to go into a place and shoot it up because this one has what might be a part of a suppressor?

        You on the bath salts?

        Who cares what someone uses to murder lots of people… they are in the act of MASS MURDER.

        • JumpIf NotZero

          Who said anything about “more likely”?

    • Nick

      Can you explain what you mean? I don’t quite understand why this would give you a suppressor and sbr on one stamp. I don’t know much about these guns either, so I’m probably missing something. But it seems to me that you would have to pay for the sbr and then if they do act as baffles, still pay to get the suppressor tube to go over them, right?

      • Garrett

        The muzzle brake is permanently attached to the barrel, making it the full legal 16in minimum length regardless of if a suppressor tube body is attached or not.

        • Nick

          Hasn’t that always been an acceptable practice, though? Like as long as the permanent muzzlebrake plus barrel adds up to 16″ it’s fine. Or are they revisiting it because this is so much shorter without it? I thought this lawsuit was over an issue of the atf claiming that the muzzlebrake, as it’s sold, dampens sound. Not over a barrel length issue.

        • Nick

          Sorry, my mistake. I understand what you mean now. It’s not an sbr, but the barrel is sbr length with a user serviceable baffle system attached that makes it a full 26 inches. Sorry about that.

  • skusmc

    Watch it SIG, that’s a nice little production facility you’ve got there. It’d be a shame if something happened to it. *wink wink


  • thumb to the nose is cool

    “related devices” reminds me of the Harrison Gear brake. Looked like the same type monolithic core 5.5″ brake, not sure how that one slid through.

    • Mr Mxyzptlk

      The difference with that though is that it is designed as a muzzle brake, and it is not designed to be readily turned into a suppressor (if you look at the geometry of the brake it would also be less effective as a suppressor than this). Whereas the brake on the MPX-C is threaded on the front so that it can be easily converted into a suppressor, and it was designed with this function in mind.

      If somebody slips a tube over the Harrison Gear brake and makes a suppressor, then congratulations, they have succeeded in breaking the law but this was not the intended use. With the MPX-C on the other hand, it was Sig’s intent to make a brake that would also be the core of a suppressor, and I honestly believe it is this INTENT that is getting them in to trouble.

      Just like with the arm brace, it is legal because it is INTENDED as an arm brace. If Sig came out with a version with a rubber pad on the back and said “you can use this as a stock if you register it as an SBR”, it would not be legal to attach it to an AR pistol.

  • Geodkyt

    Well, as ATF was just told in the LAST lawsuit where they lost in claiming a device was a silencer, when the manufacturer said it was a muzzle brake that DID NOT reduce the noise, the “features common to many silencers” argument is legally worthless.

    If it doesn’t reduce sound, it isn’t a silencer.

    The argument that this is a baffle stack is of more validity, except that Home Depot sells “baffles” by the pound on Aisle 6 — they are called “washers”. Unless this thing is ONLY useful as a silencer core, the fact that it CAN be used as a baffle stack is irrelevant (same court case).
    All Sig has to do is show that the gun is NOT quieter than it would be if you sawed that thing off the barrel, and that the device has SOME affect on the gun other than silencing it if you actually add a silencer tube (the registered part of the silencer under NFA, BTW) to it.

    • JumpIf NotZero

      True. That decision is largely at play here.

      If the ATF comes up with more substantial reasons, SIG will go ahead with the suit. Something tells me the ATF knows SIG has enough money to make this a losing battle for them. The MPX-C will likely go through. It’ll be interesting to see just hot readily they are convertible to a silencer in it’s shippable form.

      • J.T.

        “It’ll be interesting to see just hot readily they are convertible to a silencer in it’s shippable form.”

        Someone posted a video from last year’s SHOT Show. I would say fairly readily.

        • gunslinger

          ouch. this may hurt the case. in that an intended use is to become a silencer.

    • gunslinger

      intended use?

  • David

    Sig designed it so that all that is needed is a cover to turn the “brake” into a silencer. AFT defines a silencer to include the parts of a silencer. “Parts” do not need to silent the report by themselves. Since the “brake” is a part of a silencer, AFT correctly ruled it to be a silencer.

    • Emir Parkreiner

      Back in the 1980s, companies would often sell silencer parts kits. These kits contained everything but the outer tube. This is the reason the ATF included parts into their definition of a silencer, because their were solely intended to be used as silencer components.

      Muzzle brakes/ flash hiders that serve as a mount for QD suppressors, while a critical component, are not regulated as a silencer parts due to the fact that their primary function is that of a brake/flash hider and subsidiary function(s) relate to suppressors.

      • Bruce

        Wouldn’t it be nice if this whole problem went away because everybody figured out that guns that look/sound scary are still just guns. Tools for the user/enthusiast in pursuit of enjoyment and regular lawful use…

        • Daisuke0222

          Hear, hear. All of these splitting the baby arguments seem to be mandated by what amounts to a legal fiction; that suppressed weapons are inherently more dangerous than non-suppressed ones. If there were some empirical data showing a preponderance (or even a significant portion) of gun-related deaths from suppressed firearms, or that in cases where suppressed guns were used statistically more people suffered injury/death, then I think they’d have an argument to stand on.

          It certainly seems like any halfway motivated individual with a little know-how can put together a “ghetto silencer” or even machine up a decent model with readily available parts. So given that, how many crimes do we see committed with guns so equipped? I can’t recall any, and certainly in this day of 24-hour news cycles and breathless reporting on gun crimes by the MSM we’d have heard about a miscreant running around shooting people with a silenced gun. But in fact we don’t, so the whole thing just seems silly to me. Too many bureaucrats and legislators watching too much Hollywood escapist fantasy.

  • Cornelius Carroll

    I haven’t had firearm envy in a long time but I want an MPX with a silencer SO HARD right now. Damn that’s a good looking weapon and actually fairly practical for home defense too.

  • Anon. E Maus

    I don’t agree with the NFA or ATF, but it’s painfully obvious that this is a set of baffles.
    They got lucky with the Arm Brace (we all got lucky with that really), but it’s painfully obvious what they’re trying to do.

    I’d be happy to hear if they get it through, but I don’t expect them to.

  • Steve_7

    None of this “what ATF thinks” BS actually matters at the end of the day, it’s what the courts think that matters. ATF’s opinion is just that – an opinion. Courts enforce the law, not ATF. Look at what happened with the T/C carbine/pistol kits, ATF said it was an SBR kit, the Supreme Court disagreed and ATF still today (as in this case) blathers on that something that can be made into an NFA weapon is an NFA weapon – sorry, only a court can say for sure. Then there was another case where someone was prosecuted because they had an AR-15 with a full-auto carrier and other full-auto parts in it – court ruled it wasn’t a machinegun because it didn’t fire on full-auto. On the other hand, I think ATF is wrong on the 80% receivers, if your intent is to make it into a firearm, it’s a firearm at the point you start making it, imo.

    What matters is what the law says. Follow the law.

    • Daisuke0222

      I agree with your overall argument, but the problem is that ATF comes after you *and then* you get to go through the expense of defending yourself in court. The ATF can still arrest you based on their interpretation of the NFA, even if they would ultimately lose a court challenge. In the meantime you’re arrested, possibly jailed, and have to upend your life for months or years defending yourself in court, all because of ATF’s interpretation.

      It’s probably easier to spend the $200 (or whatever it is) for the NFA stamp than spend hundreds per hour on an attorney when the ATF comes after you for having parts that could be used to build something that falls under NFA.

      • Steve_7

        Not necessarily, you can go to judicial review which is what SIG-Sauer is doing here. And ATF always seems to leave wiggle room in their opinions so the enforcement division can still go after people anyway. Look at the Slidefire stock – they called it an unregulated _part_. So it still might make a semi-auto into a machinegun, only a court can say for sure.

        Too much emphasis is put on what regulatory agencies think of the law, there is a legal principle that courts give deference to the opinion of regulatory agencies, provided it is reasonably within the context of the law, so by asking the regulatory agency in the first place you might put yourself at a disadvantage in court. Which is what SIG-Sauer have done, imo.

        But frankly they’re being stupid here. Just remove the threads from the muzzle so the can can’t be mounted.

  • BryanS

    Looks like Sig is starting to point out that the Emperor’s legal clothes are just not there. I can see this having benefits to eliminating some sections of the NFA, much as the 2nd Amendment Foundation whittled away laws leading up to Heller.

  • Brian Flate

    If SIG wins this fight I wonder if there is anything preventing another manufacturer in selling a $50 crappy flashlight with a tube that just so happens to match the SIG suppressor tube?

    • Daisuke0222

      If there’s a market for it I’m sure someone will do so. Sig themselves could get into the flashlight business (everybody else is, after all). As long as the primary use is as a flashlight body, I don’t see how anyone could complain.

  • Ergo

    I hate the nfa as much as any other american, but in this case i have to side with the atf. Sig did a vid at shotshow and the only thing you had to do is screw on a solid metal tube to the end of the barrel to have a silenced weapon.

    Now if sig made the muzzle brake without threads on the end i might side with sig.

  • supergun

    I like the phrase “required burden” more like infringements against the 2nd.

  • doc300


  • Halon330

    So has anyone heard an update as to where it stands. I know the ruling was supposed to be back in August. This issue has fallen silent and I would love to see this become a reality.