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Sig MPX Copperhead Review: Best Civilian SMG?

Want a pistol caliber carbine in a super-compact pistol form? We hands-on review the Sig Sauer MPX Copperhead for reliability, form factor, price, and more.

    Rifle-like handling in a package barely larger than a full-sized pistol?

    Today’s incarnation of that philosophy is the Pistol Caliber Carbine.

    PCCs are everywhere and run both big and small. We even saw John Wick pick up an MPX customized by Taran Tactical in the latest Wick flick.

    john wick mpx
    Taran Tactical customized Sig Sauer MPX in John Wick 3

    The PCC world is currently huge but we often included big braced pistols in that same genre, and we are doing that today.

    It seems like everyone is producing one these days. We have CZ, B&T, Kel-Tec, Ruger, numerous AR manufacturers. 

    The MPX in many ways is the luxury car of the PCC world and the MPX has become synonymous with high-quality PCCs. 

    at Brownells

    Prices accurate at time of writing

    Prices accurate at time of writing

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    The gun comes in numerous configurations, including a rifle version, an 8-inch pistol variant, a 4.45 inch K variant, and now the ultra-compact Copperhead variant. 

    Now let’s get onto the full review!

    Table of Contents


    What Is The Copperhead? 

    The Copperhead is to the MPX what the Rattler is to the MCX.

    The Copperhead is an ultra-compact variant of the MPX. It’s the smallest MPX variant to date, and likely the smallest in the braced pistol PCC out there.

    FYI, this is a real Copperhead. Careful, it has spicy kisses.

    SIG likes to name things after snakes, at least when it comes to ultra-small guns. The Copperhead’s name also comes from the somewhat copper-colored Cerakote finish. Technically, it’s a coyote finish, but I get it.  

    SIG took the MPX and did everything they could do to shrink the MPX beyond even the K model.

    The Copperhead incorporates a monolithic upper! That means the handguard is fixed, so you cannot change it. To shorten the design, even more, there is an integrated stock knuckle on the lower receiver. 

    This shaves what’s close to an inch off the MPX. The Copperhead still has the Picatinny attachment point for attaching a real stock if you go SBR or the FS 1913 folding brace. The included brace is also something new. 

    SIG Calls is the Pivoting Contour Brace. This is a collapsing brace that’s identical to standard PDW style braces.

    The PCB also rotates, which allows you to strap it to your arm and rotate and move naturally. Most braces force you to conform to it, the PCB does not do that. 

    PCB Close Up

    When collapsed and not wrapped around anything the PCB comes together and present a small and narrow package. The pistol grip also comes from the Rattler. It’s super narrow and very small.

    It’s made so the end-user can draw it from a bag snag-free. 

    Sig MPX Copperhead Specs 

    We can’t talk about this gun without talking about its specs.

    This should give you a good idea of just how small this gun really is.

    The Copperhead weighs 4.5 pounds and for perspective sake, a 44 magnum Desert Eagle weighs 4.6 pounds. 

    Swampfox Kingslayer on 429 D Eagle
    Kingslayer mounted on the mammoth Desert Eagle .429 Magnum.

    The Copperhead has an overall length of 14.5 inches with the brace collapsed and a hair under 19 inches with the brace extended. It’s only a hair bigger than the famed MP5K model. 

    14.5 inches is tiny for a PCC, or SMG lite, whatever you want to call these types of guns. The barrel is a mere 3.5 inches long. To put that is perspective, the Glock 26 has a 3.47-inch barrel.

    9mm glock 26
    9mm Glock 26

    This length includes the muzzle device which is designed to propel gas and flash-forward of the shooter. 

    To finish it all off the gun is 2.4 inches wide, and 8 inches tall. 

    What’s The Point? 

    What’s the point of such a small wannabe SMG? It’s a solid question and a lot of people made the assumption this was SIGs entry into the Army SMG competition. It makes sense, they wanted a super small gun, but it turned out not to be true. 

    Side note: the Army would go on to pick the B&T APC9 PRO K, the guys at TriggerCon got some trigger time with it!

    I asked a SIG rep at SHOT Show and they confirmed the Copperhead was not their entry.

    The Copperhead was designed to be a civilian weapon.

    The design was made to maximize concealability and provide more firepower, range, and accuracy than a standard handgun. 

    It’s a gun that can be carried in a bag or kept in a vehicle with ease. It’s such a small gun that you can squeeze it into a messenger bag, a backpack, and even a small sling bag.

    Vertx Commuter
    Vertx Commuter, all packed and ready to go!

    From my own experimentation, I can fit the gun in my Blue Force Gear Jedburg pack, my Claymore messenger bag, and my Vertx Commuter

    Fits Perfectly in the Vertx Commuter
    Fits Perfectly in the Vertx Commuter

    To be perfectly clear this gun is small enough to fit in my glove box. It’s insanely easy to conceal. I also own a Desantis DSD rig, which is a shoulder rig designed for submachine guns. The Copperhead is literally the perfect gun for this rig. 

    Do I have a purpose for this gun in this role?

    Not particularly.

    To me, I could see this gun being an awesome vehicle gun when evacuating disasters like Florida’s favorite, Hurricanes. 


    I’ve been on the front line of the last two major hurricanes to hit Florida and I certainly some behaviors that showed how quickly people turn on each other.

    Luckily, I never witnessed any violence, but we’ve all seen reports out of areas where people weren’t so lucky. 

    It’s essentially a concealed carry gun that grants you more firepower than your normal CCW. 

    Breaking Down The Copperhead

    The SIG Copperhead is a unique weapon in many ways, as is the entire MPX line. However, it does share a ton of features with the AR-15. Specifically, how the controls are laid out. 

    The safety, charging handle, magazine release, and bolt release are all from the AR-15. If you’ve trained with a AR-15 you’ll have no problems translating those skills over to the SIG Copperhead. The controls are all ambidextrous as well. 

    Controls Right
    Simple and familiar controls

    A lot of things set the MPX apart, but the main thing is the operating system.

    Most PCCs run on a blowback system. The MCX runs on a short-stroke gas system with a rotary bolt. This results in a lighter recoiling gun overall. 

    The gun also comes with one 20 round magazine that’s made by Lancer and is mostly polymer with metal feed lips. The magazine is very similar to the Lancer AR mags. 

    The gun also does not come with sights of any kind. It does have a full-length scope rail across the top of the upper receiver for adding a red dot. 

    Here is where I find my first issue with the gun and that’s the inclusion of a single magazine and no sights. This is an expensive gun, retailing for around 1,600 dollars.

    A set of sights should be standard

    1 magazine…and no sights…um…

    I added a Burris Fastfire 3, which is a mini red dot that seems appropriate for such a small gun.

    at OpticsPlanet

    Prices accurate at time of writing

    Prices accurate at time of writing

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    Also, the magazines are expensive.

    They are extremely well made, but you are looking at spending in excess of 50 dollars per magazine. To me, that’s just way too high. 

    at GunMag Warehouse

    Prices accurate at time of writing

    Prices accurate at time of writing

    Available Coupons

    Unfortunately, the aftermarket hasn’t picked up the MPX just yet, and I hope in the future we’ll send 3rd party companies producing more affordable magazines. 

    The 20 round magazine actually looks very normal in the gun. The 30 rounders look disproportionate. It’s really adorable, to be honest. The magazines are easy to load though, and they never feel stiff or a pain to load in any way.

    The flash hider is permanently affixed to the barrel so you can’t add a can, or swap it out.

    The good news is this gun is compatible with all MPX barrels. Changing the barrels on these guns is actually pretty easy to do and barrels come in 4, 6, and 8-inch variants. 

    The brace comes together to conceal the strap which is another space-saving feature. It prevents anything from getting caught and hung if stored in a bag.

    Extending the brace from the gun is easy, but the brace is stiff enough that it will never accidentally extend when being stored or carried. 

    Controls Left
    Ambi Controls are really nice!

    To collapse the brace you have a small button on the wide that is a bit of hassle, but there is a point to this. That button is small because it doesn’t need to be large.

    Why would you be in a hurry to extend your brace? 

    That small button is tough to push because you certainly don’t want to accidentally unlock your brace. 

    Range Time 

    I was superbly excited to get this gun out to the range. My load of choice was Remington LE and Military Training rounds. It’s a load my local gun store had superbly cheap, especially for brass case ammo. It’s 115-grain 9mm, which should give me decent velocity even from a 3.5-inch barrel.

    at Lucky Gunner

    Prices accurate at time of writing

    Prices accurate at time of writing

    Available Coupons

    The PCB is rather interesting.

    It’s different than any other brace on the market. It’s quite effective, and very comfortable when wrapped around the arm. The way it moves allows you to utilize a standard pistol firing position. 

    If you choose to brace the PCB against your shoulder you won’t find a lot of support. The brace is also very short. The good news is that a 9mm gas piston gun doesn’t need much support. Recoil is a pleasant little push. 

    Both PCCs don’t have a ton of recoil, but there is a noticeable difference between the gas piston system and a traditional blowback gun. I fired it side by side with a CZ Scorpion and the Scorpion had significantly more recoil. 

    Because this is 4.5 pound 9mm SMG wanna be you will find it very easy to control.

    The gun barely moves.

    As we said the recoil is low, and so is the muzzle rise. You can really rip with this thing in a rapid manner and find all your shots gathered in a fist-sized group. 

    This would honestly be a great gun for younger or new shooters. It’s very comfortable to shoot and a lot of fun. Plus it looks cool and that is a major factor in attracting new shooters. 

    Accuracy wise you can extend your range well beyond your standard handgun. I started at 15 yards and used an FBI Q target and aiming for the head. I backed off to 5 yards at a time aiming for the head.

    And got all the way to 50 yards and was still making headshot consistently.

    at Amazon

    Prices accurate at time of writing

    Prices accurate at time of writing

    Available Coupons

    The Copperhead’s trigger is also outstanding.

    Admittedly it’s a little heavy, but very short.

    The reset is positive and also short. It’s basically a higher-end AR trigger, and supposedly some drop-in AR triggers will work with the MPX but this violates your warranty so I’d stay away from it. 

    Lefties can rejoice not only about the ambidextrous controls but about the gun’s ejection pattern. It ejects rounds with a forward pitch that places the projectile nowhere near the face. The ejection is consistent and this will keep lefties from eating brass. 

    Sig Copperhead Broken Down
    Sig Copperhead Field Stripped

    Reliability wise the gun ate through the Remington 115 grain goodness without complaint. It also didn’t mind aluminum cased Federal ammo or Winchester 115 JHPs.

    It’s a very accurate little gun, and the additional weight and support of the brace make it easy to stay on target. The Copperhead has certainly enough bite to go along with its bark. 

    By The Numbers

    Reliability: 5/5 

    From the first shot to shot 350, the gun has never given me issues. The gun, magazines, and parts and accessories fun like absolute champs. The Copperhead is dead nuts reliable and doesn’t seem to be fussy when it’s not cleaned. 

    Accuracy: 4/5

    It’s much easier to shoot than any standard handgun, and you’ll be impressed at just how far you can throw a 9mm pill with this gun. However, don’t expect PRS accuracy. It’s still a small gun designed with defensive use in mind. 1 hole groups at 25 yards aren’t going to happen. 

    Ergonomics: 5/5 

    The gun mimics the AR-15 via the controls, with an added splash of being ambidextrous. The controls are well thought out and easy to reach. For such a small gun it’s impressive how they squeezed it all in there. 

    Looks: 5/5

    How do I judge a gun’s beauty? By its subjective appearance? A friend says the barrel’s flash hider reminds him of a mole. It’s a hard call, but I’ll judge by the guns less subjective traits.

    The Cerakote, for example, looks great and is applied expertly. Additionally, the controls and grip are black which offsets the brown well. 

    Customization: 2/5 

    There isn’t much you can do with the Copperhead. Unlike the normal MPX, you can’t swap the handguard, you can’t add a suppressor or different muzzle device in general. You can swap the charging handle, the barrel, and Timney produces an improved trigger for the gun. 

    Bang For Your Buck: 3/5

    This is an expensive gun. $1,600 bucks is a high retail price, but it is a very well made gun. It’s reliable, accurate, light recoiling, and as far as I know, it’s one of a kind in terms of its size.

    I’d add an extra point if the gun came with an extra mag and a set of sights. 

    Overall Rating: 4/5 

    at Brownells

    Prices accurate at time of writing

    Prices accurate at time of writing

    Available Coupons

    Parting Shots

    The SIG Copperhead is an awesome gun.

    It’s a ton of fun, it’s reliable, soft shooting, and superbly small and lightweight. The Copperhead is a one of a kind gun that blends features of a wide variety of SMGs into a tiny SMG wannabe. 

    It’s smaller and lighter than most standard SMG type weapons, but at the same time doesn’t rely on its magazine being placed in the pistol grip. It’s more intuitive than those style SMGs and nearly as small. 

    Sig Copperhead and kit

    It’s incredibly fun to shoot, it really is one of the higher-end PCCs on the market. It’s refined and well-executed. I have to give some serious props to SIG. They made something rather unique in a crowded market. 

    Is the Copperhead something that appeals to you? Is it too small for you? Let me know below what you think. 

    It’s a niche weapon, but for some reason, I love these little guns. 

    Do you love PCCs? Just for the range or is your HD/SHTF gun a PCC? Let us know in the comments! If you’re interested in getting your toes wet in the PCC world, take a look at the Best 9mm AR-15 Uppers!

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    8 Leave a Reply

    • Commenter Avatar

      How can the Copperhead be practically slung? It has a single QD cup just about where the webbing of the hand hits the grip, and not much realestate on the fore end. Maybe a single point sling, but seems like the mount might interfere with the grip and also the firearm would flop around when hanging. Any tips?

      June 4, 2022 11:51 pm
    • Commenter Avatar

      It's a very attractive idea, but other than the piston there's no reason this should cost more than $700. Grand Power could make a Stribog in this size and sell it at $600, considering they sell the 8" barrel version for under $800, and it would be equally reliable with $30 mags. Palmetto State Armory has a Glock 19 clone out for under $300, and you can put an optic, laser/light and brace on it and use 33rd mags getting the same performance as this Copperhead.

      If you buy the Sig, you'd spend 1600 on the gun, 500 on a barrel (who wants something like this that can't run a normal 1/2x28 suppressor?), a couple hundred on a decent brace that won't unexpectedly come out of your bag facing upside down, and an optic before you can use it---that's over $2500 for a 9mm with a 3.5" barrel and $60 for each extra mag.

      I think I'll wait for brands with less markup to make something in this size because unless this showed up on the used market in like new condition for under a grand, the value just isn't there.

      April 27, 2020 7:46 am
    • Commenter Avatar
      Dick Wilson

      Travis, good review, cool gun, great for home or car. I own one, and have a Sig red dot on it. Do you have or would you do a video on break down and clean? Owner's manual not that clear, to me. Thanks, DW

      April 10, 2020 12:01 pm
    • Commenter Avatar
      Connor Haughton

      Sig is pricing themselves out of competition with similar platform while offering no clear unique features. Die-hard Sig fanboys are the only ones who would pay so much for such a feature-limited weapon. Proprietary mags priced at typical exorbitant Sig mag prices? There's a reason the PCC industry has largely settled on Glock magazines..... They're reasonably priced, well engineered, and many people already have a sizable collection. It's a consumer friendly decision. Shared magazines with your sidearm is a key selling point of PCC's; I have 5 33 round Glock mags for my 9mm PCC. To catch up with the MPX, it would be >$250....

      Additionally, the compactness which is the main draw of this weapon can be had in other, far more versatile, and often cheaper, platforms. Throw a LAW folding adapter on a decent AR pistol and you're coming in at half the price and a weapon that can be concealed comparably. Or better yet, get a DFA pistol or SBR and you can fire from folded configuration, while still coming in hundreds less with a more mature platform.

      The MPX platform limits you severely in terms of flexibility and customization, while not really providing much to make that a worthwhile tradeoff. That's my impression anyway, but I'm sure there are those who will be willing to invest $2k into this platform for the operator points they'll gain.

      September 23, 2019 1:05 pm
      • Commenter Avatar

        The Copperhead and MPX family does offer a unique selling point, and that's the fact it's a short stroke gas piston versus a blowback gun. In a fully automatic SMG this is likely a bigger deal due to the reduced recoil, but in semi auto civ guns it's certainly a tougher sell.

        September 24, 2019 9:56 am
    • Commenter Avatar
      Jason Birdsong

      The copperhead makes absolutely no sense. The MPX-K is the exact same gun, but the barrel is 1/2" longer and is threaded for a suppressor. And I know the copperhead barrel can be replaced but the factory barrels run over $500 a piece, that's insane for a barrel. I have the gen 1 mpx with 3 barrels, 4 handguards, 3 different stocks, and over $3500 into this system. And i would do it again this is the best PCC I have ever shot/owned. Personally I think the 8" MPX is the sweet spot for accuracy/recoil/supressor use.

      September 23, 2019 4:47 am
    • Commenter Avatar
      Charles Reeder

      Thank you for that! 1,600 bucks for a well made tool can be a life saver. Thank you for the time you spent on this review! Awesome job!

      September 22, 2019 7:17 pm
    • Commenter Avatar

      Bought a mpx 2 years ago. Had to send it back 3 times and they had it six months. Wouldn’t replace it or give my money back. I bought it for duty use. Will never buy a dog product again

      September 22, 2019 4:49 pm
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