P320 Carbine Chassis – EXO ONE From FireControlUnit

The Sig Sauer P320 line of pistols was never something that caught my attention – and it has nothing to do with the recent news events and reviews. My rationale is that I already have a lifetime supply of defensive pistols that all do the same thing (spin up the Glock fanboy and/or hammer test jokes here). However, the P320’s defining characteristic, extreme modularity, is a feature I am willing to explore. The EXO ONE from FireControlUnit.com converts a P320 into a PDW-type chassis system that will accept Sig MPX and MCX stocks, pistol stabilizing braces and accessories.

Although, the EXO ONE (X01) is still in pre-announcement mode, the specifications and features point to a  fun package. I’d like to see an SBR-ready system with an integrated vertical foregrip. Details and a signup link information are below.

EXO ONE – FireControlUnit.com

The X01 standard model can be chambered in 9x19mm Parabellum, .357 SIG, and .40 S&W by transplanting the corresponding P320 components (.45 ACP is in development, as the changes in magazine well dimensions require a specialized lower receiver). The X01 body is injection-molded in the US with glass filled nylon. The rear of the lower receiver features a vertical M1913 Picatinny rail for integration with SIG® MPX/MCX buttstocks and arm braces, such as models manufactured by SIG® and SB Tactical®. This rail can also adopt a sling attachment for outward tension stabilization, a non-shouldering cheek rest, or be left empty for concealed carry.

The X01 features an upper/lower receiver construction that attaches via the forward receiver hinge and is locked in place by a rear recoil spring guide. Models equipped with a dual-rod buttstock or arm brace will also lock together via two guide rod channels that span both the upper and lower receiver for added stability. The upper receiver features shell deflection ramps to mitigate malfunctions. Steps to clear a malfunction are identical to the P320 with the exception of working the action via the charging handle rather than the slide itself. The upper receiver was designed to accommodate suppressor iron sights.


The X01 was designed with ergonomics in mind and features an integrated angled foregrip with a substantial hand stop hook to prevent the support hand from slipping in front of the muzzle during dynamic weapon manipulation. Additional hand stops and grip accessories can be attached via the M-LOK® slots for a custom ergonomic interface. All components of the X01 are manufactured in the United States.




The EXO ONE (X01) is a patent-pending multi-caliber exoskeleton for the Sig Sauer® P320 Fire Control Unit (FCU) and adjacent firearm components including barrel, slide assembly, and magazine release. This transformation happens in moments without tools and is fully reversible.


LE – Science – OSINT.
On a mission to make all of my guns as quiet as possible.
Twitter: @gunboxready
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  • Joe

    Finally! I figured Lone Wolf or someone would do this for a serialized Glock compatible frame, but the SIG FCG is even better. Hat’s off to the engineers.

  • Brett baker

    Now we need a longslide 320!

    • Giolli Joker

      They have the X-Five version, let’s hope for an X-Six.

    • RSG

      Why, barrel length? Can use any length barrel with a normal slide. Just need lone wolf or someone similar to produce some nice 8″ threaded barrels and slide it on in.

      • noob

        mass. if you had a fixed 16″ barrel, you’d want a straight blowback bolt/slide to go with it.

  • koko

    Designer must be into russian aesthetics, because this looks a bit like SR Veresk smg.

    • SP mclaughlin

      …not really.
      You may be thinking of the AEK-919 Kashtan though, it does look like that.

  • Gus Butts


    • datimes

      I was thinking ‘interesting’.

  • I’m digging it. SBR engraving is probably a bit of a trick, but this does show how the FCU can potentially be used in a lot of different platforms. This may be a more important development than people give it credit for.

    • Bradley

      Couldnt you just register the Sig as an SBR? That way you could put it in whatever you wanted. It would be sort of like having a registered machine gun sear.

      • iksnilol

        Yeah, just engraving the FCU should work, right?

        But would be an issue what with state lines regarding NFA items. Easier to just use it in a pseudo SBR with a brace.

      • RSG

        Doesn’t the engraving have to be visible on the outside without disassembling? If so, they can just mold in a metal plate onto the frame somewhere. But as iksinlol says below- it’s best with the Sig pdw brace as shown. Slick package.

        • noob

          or cut a window in the frame that shows the serials through the side. Or cast the lower part of the frame in transparent lexan

    • Ryan L

      You do see that’s a brace and not a stock right? My guess is that with current situation these guys and the Roni guys are trying to make hay while t he climate is good.

      I would like to see a longer barrel along with the kit.

  • Bruce

    pistol caliber long guns have always tripped my fancy, this looks like a great option that I can add a suppressor to and get an SBR stamp for the Sig as well. Good times.

  • Badwolf

    Does it take glock mags?

    • noob

      actually, you could probably make a sig grip that fits the modular chassis that does have the glock grip angle and takes glock mags just to irritate everyone. Anybody got a big build volume 3d printer for the prototype?

  • Klaus Von Schmitto

    Does it take MP5 mags?

  • Awesome product idea, but man, pretty much the worst timing possible to be launching a revolutionary Sig 320 accessory.

    • Nandor

      Can’t hit the back of the frame and have a misfire if we replace the frame and add velcro straps that make drops impossible!

  • Looks like something out of Ghost in the Shell. I approve.

    • Nandor

      Yeah, the anime, not that abortion of a movie with ScarJo where they took 1980’s guns and put them in vacuum form plastic enclosures. The guns in the anime were so cool looking and they had none of them in the live action movie.

      • Hem90

        Didn’t they trade the Mateba for the Rhino? Thought that was interesting.

      • noob

        The only Seburo props available would be airsoft. Battlestar Galactica tried the airsoft versions for a while but were frustrated that they couldn’t make blank firing versions.


      • noob

        The original shirow designs were pretty cool. To make proper blank firing versions you’d have to start from scratch. In some cases the feed paths may not be physically possible due to there not being enough space for a real slide to reciprocate. justified that in some cases the rounds are supposed to be caseless or other future tech.


      • Young Freud

        I recall seeing the concept art involving the guns and WETA sure did phone that in. The worst was the MP5 they just put a box around. Like, if you want a boxy-looking tactical SMG that’s live-fire, just get a B&T APC9 or something. The sad part is that some of those guys have done GITS-inspired stuff before like Leri Greer (who got his start with the Half-Life 2 mod Neo-Tokyo).

  • Holdfast_II

    Lacks imagination. Almost a RONI – they could have made it so much cooler – longer barrel, etc.

    • RSG

      The barrel can be almost any length at all. No limitations. This is nothing like the roni as that uses the entire pistol. This just uses the fcg and slide.

  • RSG

    This is…….awesome. Throw in an 8″ threaded barrel chambered in 10MM with the pdw Sig brace pictured above and you have an excellent truck gun that can easily hide under a winter jacket, too. There are even a few leather holster makers that can make a great custom shoulder rig for this. Can even have a suppressor pouch on the weak side instead of mag poiches. Hmmmmmm. If this exo setup is less than $600, it may get me to buy a P320.

    • Joe

      “(.45 ACP is in development, as the changes in magazine well dimensions require a specialized lower receiver).”
      Gonna be a bit of a wait for 10mm, but that would be sweet.

  • Cal S.

    Why don’t any of the Glock chassis look this good?

    • JumpIf NotZero

      Because on this they can integrate the lower receiver, on a Glock the lower/frame “is the gun”.

      • Cal S.

        True, but the only company even trying is MechTech. And they’re not really trying, if you know what I mean…

  • JumpIf NotZero

    Called it.

    Good idea to use the SIG MCX/MPX shape for the lower tail, then can use the SIG stock options.

    But I’m really not fan of what they did for the upper/slide. It should be an exposed slide like the USW, which they easily could have done here, or a whole new upper like straight blowback with B&Ts hydrolic buffer or etc. They went for the cheaper and flashier option, but makes sense to actually get to market quickly, for people that like the RONI idea.

    • tazman66gt

      You would think that maybe they could have made the lower like they did and use something like a Desert Eagle type slide assembly with the barrel attached to the lower. I don’t know, but like you said, they could have made it a better setup.

  • PeterK

    HA! No.

  • inb4

    Will still go off if dropped. lol

  • b0x3r0ck

    Where do I put my light at? Atleast with the micro Roni we have a place to put a spare mag, light and laser at if we wanted.

  • Zundfolge

    Its a step in the right direction, but needs to use its own upper with a longer barrel to be good enough.

    • noob

      and giggle switch for a military offering.

  • Some Rabbit

    Just by the look of it I expect it costs twice the price of the basic pistol. Maybe SIG should stop selling complete guns and just sell the chassis and then let buyers add the parts they want.

    • PK

      That would get me to buy one right now.

    • Billy Jack

      You can find the FCU on the different gun auction sites for around $200. You can find the X-Change kits too ($300+) but pricing together you might as well buy the pistol complete. The graphic seems to show you need the slide and the FCU unless it comes with a slide.

  • RogUinta

    “The upper receiver was designed to accommodate suppressor iron sights.”

    Apparently someone knew I might be interested!

  • FOC Ewe

    Poor Man’s B&T USW…. Kinda neat.

    • JSmath

      USW’s just a poor man’s long gun. This doesn’t seem like a step down in any way, honestly.

  • Dickie

    So its like the micro roni. Still like the idea. Would rather it come from sig but all good

  • john huscio

    Great, something bigger to drop….

  • Friend of Tibet

    damn, that’s one cool design

  • Darren Hruska

    Wouldn’t that integrated “vertical foregrip” (it’s more of a safety feature than anything) redefine the gun as an SBR by itself? If that’s the case, then you’re probably better off going with a stock than a stabilizing brace. I’d love to see a variation of this that’ll still classify as a pistol.

    • Pete – TFB Writer

      Technically AOW with a brace. But yes, that’s what I was thinking. Stock with VFG for SBR fun.

      • Darren Hruska

        Now, that confuses me. I thought braces didn’t transform pistols into NFA items? I know there was all of that confusion and hysteria a few months back, but that was really an “opinion letter,” if I recall correctly. And I believe the ATF retracted that since.

        • Pete – TFB Writer

          AOW because of the VFG…

    • JSmath

      No. There is no VFG. Refer to all the knowledge and documentation on angled foregrips not being VFGs.

      • Darren Hruska

        Ah, sorry. I thought I read “vertical” at first. My bad.

  • Sledgecrowbar

    Nice use of the modular receiver but it’s a lot of effort to gain a stock. I’d like to see a 16″ barrel with fore end to match.

  • Paveway

    Does it fire when dropped?

  • TW

    But is it drops safe???

  • nova3930

    If someone makes a longer barrel I’m in for another pcc

  • Veritas

    You don’t like the 320 because you have a lifetime of defensive handguns? What the Fudd? Why are you writing for a gun blog that writes about new defensive handguns? I wouldn’t say Glock fanboy as much as I would say everything handgun for you was made in the early 1900’s. What kind of car do you drive? 1970’s Lincoln?

    • Pete – TFB Writer

      I think you are taking my one sentence way too seriously. I don’t own a 320 because I can’t carry it on duty and it doesn’t do enough differently than the 10 other defensive handguns I own. In short, it doesn’t do anything for me.

  • LazyReader

    First Roni for Glocks
    EXO for Sigs
    what’s next, hopefully something from S&W for………….M&P

  • LazyReader

    Just think: For the price of a second pistol, you too can add three pounds to your pistol and prevent it from fitting into any of your holsters… without increasing it’s capacity, rate of fire, or barrel length!

  • Cap’n Mike

    An idea with limitless potential.

  • kalashnikev

    That’s the “full potential?” Years ago, dudes were mating F/A MAC lowers onto RPDs, and the best thing these guys can do with a serialized FCG unit is to turn it into one of those Glock-a-roni things???

  • Brad Schultz

    How much does this kit cost? Between the price of the pistol and the kit couldn’t you get a Sig MPX?

  • Maximilian Johannes Benning

    No listed suggested retail? that mean’s it’ll be expensive. I’m betting about $650.

  • Intellectual Slacker

    I had this as an idea even before the B&T USW (Their idea to simply serrate the front of the slide is genius) for glock pistols and when the P320 came out I new it would be a much easier task because of the FCU design and the frame not being serialized but imo going about it in a simpler minimalist way like the USW is a better way: either a polymer, aluminum or hybrid frame with a folding and an ak style side optic mount. And since the P320 is already equipped with front slide serrations charging the weapon is the same as the USW.

  • noob

    been waiting for this to show up. Now we need a 16″ barrel which is fixed to the shell and a heavy bolt/slide assembly that operates on straight blowback to eliminate barrel tilt engineering angst and you have a very handy little carbine that can use a real collapsible stock (sans tax stamp if the whole thing meets OAL requirements).

    And you can then reap the benefits of nearly 1000J muzzle energy from ordinary ammo like 9mm para or 22tcm9r in the longer barrel.

    • Cymond

      OAL is measured with the stock fully extended, per ATF guidelines. Just give it a really long sliding stock.

  • Anthony “stalker6recon”

    Just a guess, but the exo probably costs twice as much as the pistol itself. Don’t get me wrong, it looks nice and all, but seems to be taking a pistol to a whole new level, which is already filled with factory made weapons, like the MP7 and other SMG’s. That is what this looks like to me, just a frankenstein that might be fun, but I would prefer to buy something that is intended from day one, to be an SMG.

    But don’t get me wrong, I will always accept one of these as a gift! Buying anything firearms related in the Philippines, is always ridiculously expensive and painful, they don’t like guns in these parts, that is why the black market is twenty thousand times bigger than the legal one.

  • AUTiger89

    Will it work with the P250, since the frames are common between the P250 and P320?

    • Kent Yud

      Yes it will work with the p250 model

  • dustin means

    Will it be compatible with the RX models?

    • Kent Yud

      RX or RMR will not fit within the upper receiver

  • Richard Lutz

    A little surprised to see what a neat idea this is. That said, if you want a tactical long gun you should be using an AR or AK and stick with that, not have two different long gun platforms as doing otherwise could cause a fatal delay in a life-or-death situation.

  • PaulWVa

    I want this. I have two 320s…so two FCUs….I think one could find a home here….yes, I want this.