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SIG SAUER was at the second annual Texas Firearms Festival, and they brought along something new: their 16 inch carbine version of the 9mm MPX. The original plan was to have a gigantic muzzle brake on the end of a normal barrel, but the ATF put the┬ábrakes on that idea for now. While SIG SAUER and the ATF battle it out in court, they’ve decided to bring a rifle version of the pistol caliber carbine to market anyway using an actual 16 inch barrel. There’s just one hiccup: this is the “Gen II” version I talked about in my review of the MPX.


As seen at the TFF, these are the two variants of the MPX side by side. There are three big differences, the first being an extended strengthening plate on the side of the receiver. The second big difference is that the feed lips are elongated on the Gen II magazines and (according to SIG SAUER) will not be backwards compatible with the Gen I guns. This again proves my statement that the GEN I guns might not be getting the caliber conversion kits, since there are some definitive differences that are incompatible between the two guns.

The third big change is a little less obvious.


The ejection port has been enlarged for the new calibers.

Needless to say we’ll be getting our hands on one for a review as soon as possible.

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  1. Kinda butthurt because we just bought one a month ago…
    Also, any idea if the uppers could just be swapped out and called good?

    • The gun you bought a month ago is just as good as it ever was. Apparently you thought it was worth the money a month ago.

      • You don’t understand: the upper on my gen 1 is defective and I’m likely to send the entire system back under warranty.

        Perhaps this clears up why I’m a little butthurt about purchasing so recently in light if sig releasing the gen 2’s.

      • I think his problem might be with the fact that the caliber conversion kits that were promised in the future might not even come out for his gun. This is like buying a game console and only being able to play the games that came out in the first year.

    • I own three Sig pistols, the first dating to 1984, and I don’t have that impression at all. The 226, 229 and 239 have not had any revision that renders my version obsolete, and I’m not sure that I would care if it did. My 226 doesn’t have a rail, but rails were not available on anything when I bought it. And while a rail might be nice it doen’t do anything for my application. What I mean is, I ain’t gonna sell it and run out and get a P226 with a rail!

      I am somewhat concerned with Sig’s prolific product line, and wonder how they keep up with production of 26 different versions of the P226. But as long as the product satisfies me I ain’t gonna worry about it.


      • Of course you don’t have that impression!

        The SIG that made the pistols you have was a totally different enterprise in comparison to the one you have now. Old SIG was a stalwart producer of (basically) the same pistol; P226 derived guns in various permutations and flavors. That old SIG is dead because – honestly – the P226 was usurped by Glock and polymer frame/striker fired pistols about 20 years ago. While there will always be a market for precision made, aluminum framed, hammer fired, old-school DA/SA SIG pistols, that market is quite limited and not strong enough to support a large enterprise.

        New SIG is rapidly taking the place as *the most innovative* firearm manufacturer in the industry right now. They are making more premium stuff than Ruger (also kind of innovative), they are making better stuff than KelTec (innovative, but crap execution), and they are rapidly usurping HK as the innovative Euro gunmaker (entirely HK’s fault; as excellent as the VP9/40 are, it’s too little, too late). The MPX, MCX, P320 are interesting, highly innovative designs and whole new weapon platforms.

        But yea, the downside to SIG’s innovation is that new users are basically beta testers on all this stuff. It isn’t like SIG doesn’t test these things before release, it is that people have little appreciation for just how complex modern manufacturing is when your components are this complex. It is kind of a downside, I don’t think anyone at SIG is a fan, but it is the price that is (apparently) to be paid if you want to be an amazingly innovative firearms company.

  2. Too many Sig products have required major updates in recent years: P290 to P290RS, P250 to P320 and now the MPX to MPX gen 2. (Full disclosure: my EDC is the P290RS.)

    The magazine change also confirms something I suspected a few months ago when browsing the Sig site for the MPX and accessories and saw a note on the MPX magazine page which seemed odd: (paraphrasing) the mags were for current production MPX’s only.

    • The P250 was not “upgraded” to the P320. While visually and conceptually similar, they’re both different guns and are being produced side by side to fill different user niches.

      There were, however, 2 generations of P250s.

    • Interesting. I hadn’t heard of the P290 before today. I checked it out on Sig’s website, and I don’t think I want one. Polymer + striker fired = no sale.

      I thought, initially, that you were talking about the P229. I have one of those in the new version (R, or E2, or something like that). From what I understand mine is back compatible with the original, but I really couldn’t care less. I have firearms that are well over 100 years old, and any “upgraded” version of that happened to be made doesn’t really matter. They were useful and functional in their time, and they are what they are. I don’t buy firearms hoping that they magically gain new capabilities.

      • The P290RS is a hammer-fired, double-action-only single-stack handgun without external safeties. The RS stands for Re-Strike which allows a second try at firing a round without partially racking the slide first as was required by the original.

    • Yeah, my thoughts too. Every time I see a new product (especially a Gen 1) I make a mental note to check back in a year or two.

      But I favor my ARs, 870 and 1911. Go figure.

  3. I got one of the first ones I think and mags are hard to get …if they are making gen 2 mags that won’t work with gen 1 I’m shit out of luck my form 1 just came back on my mpx..I hope they can do right by this some how

  4. All right, let’s not play games.

    We’re talking about a 16″ MPX carbine, not an SBR, yet the second picture clearly shows an SBR (why?).
    Did you remove the barrel shroud from the Gen 2 carbine for the pics? Why?

    I ask because I’m in the market (tough titty CZ Scorpion) and I nearly bought one last night on GB (listed as Gen 2). The pics clearly showed a 16″ shrouded barrel without the queer baffle crap on the muzzle (because I’m not interested in gimmicks) and a collapsible stock.

    So what’s the deal?

    • The SBR in the second and third pictures is a Gen I and it is there to show the differences from the Gen II rifle sitting next to it.

      • In the first picture there are three firearms and a barrel shroud. It is unclear if the barrel shrould came off the MPX pictured without a barrel shroud, but I don’t believe that it did.

        Taking a little bit more care in the photo compositions for this post would have greatly increased its clarity.

  5. Ummm, OK. Why? Is there really a market for a $1400 9mm carbine? What can this carbine do that a $600 Olympic K9 can’t? I seriously considered an MPX after finger humping a Scorpion in my LGS and immediately knowing that I would never take it seriously enough to use as anything other than a toy at the range. I have two in college so I don’t buy toys anymore sadly.

    Then I picked up on the fact, thanks to the TTAG fanboi review, that even though it was a year late it wasn’t quite right and decided to back off. I was conflicted for other reasons too, no forward charging handle? $1400 for a gun that you had to immediately replace the trigger in? $50 magazines? How about a 10mm (which I could hunt with)? 45?

    I’ve said it before and will say it again…Sig repeatedly proves that it is amateur hour in their product management, marketing, and sales management groups (based on discussions with local LGS owners). Their product launches aren’t taken seriously by anybody. I don’t know anything about the “gun business” but man, it can’t be that hard. I have friends at Sig, love NH, and want to “represent” by owning a couple of Sig products but they make it so damn hard. I am hoping they get their $hit together with silencers but I am waiting to purchase one to avoid getting burnt like the gen 1 MPX owners appear to be.

  6. I decided to get some clarity, as I have a Gen 1 MPX and want to put a .40 cal upper on it. So, I talked to Tim in Sig’s Customer Service Department. Here is what I learned:

    1. They will offer both Gen 1 and Gen 2 9mm magazines and will specify which is which going forward, as Gen 2 magazines will indeed not work in Gen 1 guns.

    2. The .40 cal Gen 2 upper will work on Gen 1 9mm lowers. The .40 cal Gen 2 magazine will work with the Gen 1 lower.

    3. Sig will offer Gen 2 uppers to Gen 1 owners at a considerable discount.

    4. We agreed that an upper swap is better for a caliber change, as the zero on sights and optics flies out the window during just a barrel/bolt change. We both thought that having a dedicated and separately mounted/zeroed optic for each upper was a better option.

    5. We agreed that having a Gen 1 lower registered on a Form 1 was a significant reason for them to have Gen 2 uppers to be compatible with Gen 1 lowers.

    I hope this helps someone somewhere.

    • Just wanted to affirm what the guy above me said and further reinforce SIG’s claim. I talked to Josh over there and the following are his high points:

      – GEN II uppers will fit on GEN I lowers
      – MPX GEN II currently isn’t for sale over the phone, looking at Q1 2016 for that
      – Current (GEN I) owners of the MPX will be able to purchase the GEN II upper at a discounted price (roughly the same as their Caliber X-Change kit). This is about 600 USD based on what I got from him
      – GEN II uppers will be able to accept the GEN I barrel and bolt
      – GEN II is .40 S&W by default; you’ll need to purchase the conversion kit to get the .357 SIG.

  7. Well, SIG just killed their argument that they had to do their short barrel with the pinned baffle stack/”compensator” because the gas system in the MPX wouldn’t work with a longer barrel. Oops.

  8. So answer this for me. I have a Gen 1 sbr. Can I use Gen 2 magazines and a Gen 2 upper? As in the lower is the same between generations so either magazine will work with the lower but not the upper?

    • According to the people who have called SIG and asked, yes, and people who bought Gen 1 guns will get a discount on the Gen 2 uppers.

  9. I think some people are under the assumption that the lower is different between generations and will only accept their specific magazine. That would be a problem for sbr lowers but as I understand it all magazines fit the same lower but the not necessarily the upper. Not a big deal for me since I can buy another upper if desired.

  10. SIG has Gen 2 Magazines coming out and can’t fill the orders for the Gen 1 mags. Something is wrong there.

    Same with the stocks. They can’t fill the orders for current products but are rolling out versions 2’s of the same platform. Makes zero sense from an operations standpoint. Want to bet they will have no problem finding stocks for the “new” production models to ship. I feel like I got conned.

    So if you bought a Gen 1 MPX you can’t put a Gen 2 upper on it in 9mm and you have to hold out hope that you will be able to get Gen 1 magazines and parts that wear out for your GEN 1? You also have to hold out hope that one day they will ship the backordered stocks and magazines before they are discontinued in favor of Version 2’s that won’t fit your earlier platform.

    I don’t think I’ll be buying another SIG anytime soon. What a night mare this has become.

    • I will have to emphasize that, according to SIG, your comments are inaccurate. GEN II uppers will be compatible with GEN I lowers, and GEN II uppers will accept the GEN I 9mm barrel and bolt assembly.

  11. Bastardized AR lower converted to use pistol calibers.
    Retarded AR charging handle.
    No 10mm.


  12. I feel cheated. I got the early version MPX vs other much less costly 9mm carbines solely on the premise of its inexpensive convertibility. The barrel length and caliber change were to be EZ and inexpensive was the selling point. I see now that it was a election type lie.
    Also the upper I have literally looks like it was used dry with sand added. It shows excessive wear. After only 5 mags of nonsupresed use it looks like 5000 rds or more of supressed wear. It’s like the aluminum was not hardened. I have never seen wear this extensive in guns I have owned for over 30 years and yes I run it wet and lightly greased in all the friction areas.

  13. I see the same complaints about this firearm everywhere, but they aren’t complaints about the firearm itself. They are complaints from people who don’t own it, complaining about what they would change.

    “No 10mm”
    So what? You know why there are barely any 10mm carbines on the market? Because there is barely any market for them. But, there are a few 10mm carbines in production, and you complainers probably haven’t bought one of those either.

    “AR charging handle”
    Again, so what? I haven’t ever heard a single person say that they wouldn’t buy an AR because of the charging handle design. But, chamber a similar design in 9mm, and all of a sudden the charging handle is a major design flaw? (I see how it could be awkward with the pistol version, but this article isn’t about the pistol version, and the pistol version is pointless anyway, IMO)

    “Why pay X for this firearm when I can get this other firearm for less than X?”
    Yeah, go ahead and get that other firearm, then. You can get a Ford Focus for a lot less than a Maserati GT, too, but that isn’t hurting Maserati sales. You just aren’t in the market for the Maserati..

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