SIG MPX Copperhead review
Mitch Hardin for TTAG
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By Mitch Hardin

Origins of a Copperhead

SIG SAUER officially released the MPX Copperhead Pistol at SHOT Show 2019 in Sin City, USA, this past January. Some may be curious where the “Copperhead” name came from.

According to SIG SAUER, the MPX Copperhead was a project developed very similar to the Rattler SBR. The goal here was to create the smallest possible platform, while reducing snag points, and maximizing concealability. It name also has to do with the custom Cerakote color that adorns each and every Copperhead.

SIG MPX Copperhead review
Mitch Hardin for TTAG

The Copperhead has a 3.5” barrel with an integrated muzzle brake to prevent gas from blowing back into the handguard, or onto the shooter. We were informed that any MPX 9mm barrel will work on the Copperhead.

Shooters wishing to utilize, say a SIG SAUER suppressor, or any can for that matter, are going to want to opt for the 4.5” “K barrel.” That will allow you to utilize the threads to mount a can if you so desire, or your favorite muzzle device.

SIG MPX Copperhead review
Mitch Hardin for TTAG

Recently SIG released a version with a 4.5” “K barrel” for government agencies, with public sale soon to follow. SIG will also be releasing a version as an SBR with a functioning stock. As it stands, you can get a “2 position pistol contour brace” (as shown), or a folding pistol brace.

SIG SAUER was very specific in mentioning that the engine driving the MPX Copperhead is the same exact system as all other gen 2 MPX’s. No changes were made to the platform itself, only aesthetics. That’s important, as everything needs updating now and again, otherwise we would be talking about “tactical flintlock pistols.”

SIG MPX Copperhead review
Mitch Hardin for TTAG

The MPX Copperhead was designed in part from a customer who was looking for a lower cost version of the MPX that had additional features, but didn’t sacrifice its most important feature, its closed rotating bolt design. Add in the fact that the MPX Copperhead is fully ambidextrous, and you have a serious contender in the personal defense market.

However, as a SIG SAUER rep told me, this version of the MPX Copperhead Pistol (3.5” barrel) was primarily intended for personal defense, to be carried discreetly in a small bag, or in your vehicle (as and where legal, of course).

SIG MPX Copperhead review
Mitch Hardin for TTAG

While SIG SAUER listened to customer input, they also listened very intently to the “professional community.” We were informed that many government contracts have already been awarded for the MPX Copperhead. Primarily the U.S. Armed Forces, and its desire for a compact, lightweight, sub gun in a pistol caliber.

Every Bit as Poisonous as its Name

This little fire breather uses a monolithic upper and integrated lower knuckle, with a 2-position pistol contour brace (PCB). Based on customer input, SIG developed the PCB with the intent of making it easier for the shooter to get down on the sights and maneuver without having to lock your arm out straight. The PCB pivots to provide comfort for the user as they are shooting and moving, while ensuring a better pistol shooting experience.

SIG MPX Copperhead review
Mitch Hardin for TTAG

While the MPX Copperhead may look similar to an AR-15 modern sporting pistol, that’s about where it ends. When you separate the upper and lower receivers, you will instantly see the differences.

The two platforms are more like “cousins” if that helps. There is no buffer tube, as the SIG MPX design uses a twin spring recoil system that rides over the bolt, and under the charging handle.

SIG MPX Copperhead review
Mitch Hardin for TTAG

What helps define and set apart the MPX Copperhead from its competition is that SIG went with a tried-and-true short-stroke gas piston with a closed rotating bolt design. SIG states it has been extensively tested and professionally used in the PCC competition community.

If you also take note at the rear of the MPX Copperhead, it has a vertical 3-slot Picatinny rail built into the lower receiver. This allows the shooter to mount any type of sling attachment that they so desire, making it very versatile.

SIG MPX Copperhead review
Mitch Hardin for TTAG

Customizing & Concealment

As far as accessories are concerned, SIG SAUER seems to have this area covered. There is a steady aftermarket selection as well.

The operating system is the money maker for the MPX Copperhead. SIG SAUER states that they have spent years perfecting and modifying this design in an effort to make it “more reliable than any blowback system on the market today.” They chose a tried and true closed rotating bolt design, along with SIG’s legendary gas piston for a cleaner, and cooler running Copperhead.

SIG MPX Copperhead review
Mitch Hardin for TTAG

Also noteworthy is that AR triggers will not work with the MPX line. However, there is a good aftermarket to support the MPX Copperhead, with options from companies such as Timney, Mid-West Ind., and Lancer to name a few. With aftermarket support like this, you can swap triggers, handguards, etc., and that’s not even counting all of the SIG SAUER branded swappable parts.

SIG MPX Copperhead review
Mitch Hardin for TTAG

I’ve had the opportunity to test many 9mm pistol caliber carbines, and can tell you without a doubt that the MPX Copperhead is one of the most concealable 9mm PCC’s in its class. If your spouse carries the kitchen sink in their purse, this too should fit in there alongside the spare roll of TP, and the 15-20 pens at the bottom.

I successfully fit the MPX Copperhead into many smaller handbags that a woman might use. I personally use a Drago Gear “Tracker Backpack” on a daily basis (above) as my Jeep lacks a top and doors for half of the year.

For a daypack, it carries everything I need, including the Copperhead. It’s like it slithered its way in there, and it fits like a glove. Not only that, but it fit loaded while with a 20-round magazine inserted. There are plenty of other pockets in this bag for more reloads as well.


SIG MPX Copperhead review
Mitch Hardin for TTAGThe  

The Copperhead ships without sights allowing you to choose irons or an optic. As an aiming device, the Holosun HS515CU was chosen for this review rather than iron sights.

Given past experiences with other Holosun optics, there were no worries here. This thing has a 50k hour battery life, using a simple CR2032 (watch battery). It’s green LED projects a clear, crisp 2MOA dot inside a 65MOA ring. The user has the option to use either, or both. The Holosun HS515CU is a parallax free optic with unlimited eye relief.

One of my favorite features is the “Shake Awake” option. In a nutshell, it goes to sleep shortly after you set your weapon down. The vibrations of grabbing said weapon will immediately shake it awake and project its green dot. It’s like it never went to sleep in the first place. Made of 6061 aluminum, it can take a serious ass beating. But that’s for another article entirely….

SIG MPX Copperhead review
Mitch Hardin for TTAG

Shooting In A Polar Vortex

Range time with the MPX Copperhead was a blast (pun intended). We had been hit with a Polar Vortex that swept across parts of the Northern U.S. and Canada this past winter. Single digit temperatures with wind and blowing snow seemed like the “logical” time to go out and do some shooting.

SIG MPX Copperhead review
Mitch Hardin for TTAG

The Copperhead was subjected to approximately 750-ish rounds, consisting of a mixture of HP, FMJ, TMJ, pretty much whatever I could find to feed it. It was dropped in the snow, kicked around, chambered, and then fired like a boss.

Reliability was never an issue as the Copperhead kept digesting ammo without hesitation, and putting rounds on target. Here’s what I fed it:

[Bullet weight measured in grains, velocity in FPS by Caldwell G2 Ballistic Precision Chronograph at 15 feet, and accuracy in inches for best five-shot groupings at 20 yards from a Vanguard Scout Shooting Stick.]

Velocity Accuracy
Hornady Critical Defense 115gr. FTX 1060 FPS .58”
HSM 115gr. Hornady XTP 1190 FPS .62”
Sig Sauer Elite V-Crown 124gr. JHP 1167 FPS .56”
Wilson Combat 147gr. RN 781 FPS .56”
Speer Lawman 124gr. TMJ 972 FPS 1.1”
MEN 124gr. FMJ (NATO) 1004 FPS .91”
American Eagle SYNTECH 115 TSJ 1075 FPS .91”
Federal SYNTECH 150gr. TSJ 836 FPS .77”

Speaking of targets, every load tested came in under 1 inch in group size, save for one, which was just barely over 1 inch. SIG SAUER Elite V-Crown 124gr. JHP netted us a .56-inch grouping at just 20 yards. Now, one might think, “Why only 20 yards?”

Realistically, 60 feet (20 yards) is more than enough distance to wring out a sub-gun type of pistol with a 3.5” barrel, especially for a “defensive situation.” In the interest of full disclosure, a Vanguard Scout Bi-Pod Shooting Stick was used to help net these results. It just goes to show us how accurate this little fire breather can be.

SIG SAUER informed us that they tested the MPX Copperhead extensively using what they call “DV Testing” (design validation). SIG’s “DV testing” consists in part by using 10-15 random examples, and running them through environmental, endurance, safety procedures, and ammo compatibility.

SIG stated that they conduct these tests on every platform they design so as to exceed expectations of their commercial and professional customers. I see no reason to doubt those claims, as the MPX Copperhead more than met expectations during testing.

SIG MPX Copperhead review
Mitch Hardin for TTAG

The representative from SIG SAUER that we spoke with also stated that their intent with the MPX Copperhead was “to offer the market a sub gun that was easily concealable for situations where people would want a self-defense weapon that was reliable, easy, and quick to deploy.” Given what we’ve seen and experienced with the SIG SAUER MPX Copperhead Pistol, it’s safe to say that SIG SAUER hit that design goal.

If you are looking for a fun range gun or defensive weapon, the MPX Copperhead has a lot to recommend it. Given its compact pistol form, one can easily take it on the road when traveling, provided you have all the necessary legal “PAPERS, PLEASE!” Given its concealable size, the MPX Copperhead Pistol makes a great travel buddy. Judging by our results at the range, I’d say they that the SIG SAUER MPX Copperhead Pistol has plenty of venom.


Operating system: Gas piston
Caliber: 9mm luger
Capacity: 20+ rounds
Overall length: 14.5 inches
Overall width: 2.4 inches
Height: 8 inches
Barrel length: 3.5 inches
Weight: 4.5 pounds
MSRP: $1835 (about $1580 retail)

Ratings (out of five stars):

Style * * * * *
An American classic. The American classic? Could be. It’s one cool little gun.

Fit and Finish: * * * *
The “Copperhead” custom Cerakote paint used on the pistol is very tough. Mine scraped across some barbed wire and came away looking just fine. SIG SAUER did a very nice job on this one.

Accuracy * * * * *
It’s hard to argue with the results. Twenty yards was more than a realistic distance for a personal defense pistol of this design. The SIG SAUER Elite V-Crown 124gr. JHP came ripping out of the barrel at 1167 FPS and scored a just over a half-inch grouping. HSM 115gr. Hornady XTP netted 1190 FPS and .62 inches. That’s hot and fast accuracy headed towards bad guys.

Ergonomics * * * * *
While the SIG MPX Copperhead pistol is certainly small, it feels good in the hands with no sharp edges or other concerns noted in that respect. It’s very “AR-ish” as far as ergonomics go, and that’s a good thing.

Reliability * * * * *
I’ve been playing with the Copperhead for a while now and have no long-term reliability concerns. It’s eaten everything I’ve fed it, and it loves an ice-cold meal.

Customize This: * * *
Ambidextrous side charger?

Overall * * * * 1/2
The SIG SAUER MPX Copperhead is an impressive little pistol. Especially given its cold weather performance, and punishment during that Polar Vortex we endured. While it’s full-featured out of the box, a threaded barrel would be more useful, and efficient. While it isn’t inexpensive, it makes for a great Jeep or truck gun for those who have the valid “Papers, PLEASE!”

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    • Um, yeah.

      If you’re limited to semiauto, there are far better ways to launch 9mm out of a 3.5 inch barrel.

  1. SIG Sauer MPX Garter Snake

    “Integrated muzzle flash hider” thus ensuring no useful accessory such as a silencer can be added.

    Everything this gun can do, a B&T (any of their SMGs) can do better.

  2. I see plenty of utility and uses for pistol caliber carbines… just not this one. A 3.5 inch barrel is just too short. Why bother carrying this instead of a compact handgun? You’ll have better ballistics from a Glock 19 sized gun. Sure, I get that you can shoulder this and possibly be more accurate. I don’t feel that’s a worthwhile enough trade of compared to all of its negatives.

    • Also, a recoil action makes more sense in a package this small. It’s impressive SIG can get a gas 9mm to run with so short a barrel, but a recoil action (Glock in a chassis, USW, X-01, MP9) will be even smaller & lighter, in an application where size & weight have priority. For the MP9 at least, all the moving parts are internal as well, so there’s no reliability drawback.

      Same goes for using a pistol-grip magwell.

  3. For about two seconds I was confused as to which way the gun was pointed in the top image. I briefly couldn’t tell which was the grip and which was the magazine and also the barrel from the stock. I’m sure it functions very well but I think I’ll pass on this design as I get vertigo just looking at it. First time this optical illusion effect has happed to me with an image of a firearm.Very disturbing sensation!

  4. It is hideous, expensive, and has a barrel shorter than regular full size handguns. I have been wanting a vehicle/ backpack gun and the CZ Scorpion seems like a superior option in every way.

  5. ‘ SIG SAUER that we spoke with also stated that their intent with the MPX Copperhead was “to offer the market a sub gun that was easily concealable for situations where people would want a self-defense weapon that was reliable, easy, and quick to deploy.” ‘

    I guess pistols aren’t good enough for “reliable, easy, and quick to deploy.” Not at all like a tiny rifle that you have to keep in a bag on your back. That’s way easier than a pistol in a holster on hip.

  6. What’s with the cost of these things? Locally Scorpions are going for over $1,200. Is it just trendies inflating prices? No way a polymer 9mm should command a price higher than a nice magnum bolt gun for instance.

  7. “Also noteworthy is that AR triggers will not work with the MPX line.”

    Is this a typo?

    I’ve been running a Geissele SSA-E in my MPX-K since I got it in mid-2018 without any issues. In fact, I took it directly out of my Colt M4 LE6920 and dropped it right into my MPX-K.

  8. These seem to be well made and made for a purpose.

    Unfortunately money is an issue for me, so I’m stuck with my Ruger pc9 doing the same job in a slightly bulkier package. It takes my Glock 30 round magazines though, and comes threaded from the factory. It’s more than 3x cheaper as well. I understand they’re not the same target demographics, I just can’t be dropping $1,500 plus on any 1 gun for the foreseeable future.

  9. I can’t disagree that a good pistol can do the same job. But I would say that a “real” copperhead would be for professional use and be full auto. An HK MP5 has been an icon for most of my life. A semi-auto MP5/clone is also expensive and does nothing more than a good pistol. But some of us like to have affordable ($1500) semi auto copies since we cannot afford the $20 or $30,00 for the real thing.

  10. There’s one sense in which these could make sense… maybe: if it had a select fire switch with a relatively slow churn, or a three round burst. Then it could fulfill something useful that a duty-sized handgun would be hard to match. Of course, that is not on the menu for non-SOTs and LEOs like us inferior ordinary citizens. But even if we could buy it in select-fire… it’s still a niche weapon (and as such, I think everyone is puzzlee by the non-threaded barrel…). Perhaps it would be useful for disabled or injured people who find it easier to two-hand and shoulder a larger, more stable platform. Perhaps under severe stress, it is easier to aim and control… who knows. What is clear is that t’s a 9×19 PDW with the ballistics of a compact carry gun– whatever the purpose it serves for $1600 bucks, that purpose is undoubtedly specifically specialized to a specific specialized user. On the other hand… if you were in a parking lot gunfight with a barrel of yahoos, would you rather have a garden variety Glock or Beretta, or this MPX with 20-30 round magazines and a red dot or reflex sight, nice and snug on the shoulder? I gotta be honest– maybe… and I’m not a bad pistol shot. I doubt I’d be worrying about the price tag in the thick of it. So, it’s for somebody to make use of….

    All said… generally speaking, I am all for a healthy, robust American arms market with buttload of choices. I think more choice in everything is good. More SIG variants are good. More braced pistols– and companies constantly pushing that envelope of what a “brace” is– are good. More normalization of defensive weapon platforms that are not simple “one-handed” pistols is good. More acceptance of super-duper assaulty-looking military-esque civilian arms is always good. More buffoonery by amped up Americans looking goofy playing Tier One Operator is… never mind. But mostly… everything about more cool guns in more cool variations is a good thing. I ain’t gonna buy a Copperhead; I’m all set with PCCs and PDWs, and I have different set-ups at a way different price point. But if you come out shooting with this, I won’t laugh at you, hardly… I’ll ask you if I can try shooting it. 😁 It’s your money, and you need what you need, so buy whatcha want. God bless America.

    Be safe. Mort AZ

  11. There are a lot of better guns for 1500 to 1800 dollars. In fact you could buy two guns for that much.

  12. Seems like it might be a cool toy at half (or maybe a bit more, but not much) that price.

    At this price though… Yeah I can’t see it.

  13. My ASR 9mm isn’t quite as small or as accurate, but it’s stone-cold reliable and it uses ubiquitous Glock mags, and it cost just over 1/3 the street price of this Sig.

    Still, I do love me some Sig. Even when I can’t afford any more of them.

  14. This article reads like sponsored content. I even scrolled back to the top halfway through to make sure I didn’t miss a sponsored content tag.

  15. 3.5″ barrel kind of defeats the purpose of a rifle . . . . unless we’re talking about suppressing it.

  16. The charging handle is the worst part of the AR platform. Why do companies keep incorporating it into their designs?

    • Because it’s ambidextrous, it doesn’t get hot, and it allows the side of the receiver to stay closed.

  17. For all the haters that compare something like this to a Glock, they really aren’t in the same class. Yes a normal pistol is more concealable and yes you can buy 3-5 for what one of these cost. That doesn’t make a normal pistol better. They are very different. Small sub guns / PCC like this are much easier to make hits with than a normal handgun. Headshots at 25 yards are very easy and are doable at 50 yards and beyond with just a little practice.

    The real comparison for something like this is a Scorpion Evo Micro, which runs about $1100. So $600 cheaper and magazines are about half the cost at $25 vs $50+.

    The advantage the Sig has is that with a gas operated system you have a lot less reciprocating mass, which can make a big difference when you are trying to shoot fast.

    As for the Copperhead vs other Sigs, I think the MPX-K is a much better gun for almost everyone. The barrel is 4.5” long + it has a small A1 type flash hider, so it’s probably only 2-2.5” longer than the Copperhead. It also has a slightly longer hand guard and comes with a full sized pistol grip compared to the weird Star Wars blaster grip the Copperhead has. The MPX-K runs around $1700 with the collapsible brace. This is expensive, but still slightly cheaper than a MP5k clone from Zenith/MKE or PTR and the ergonomics are much better.

    • Thanks for a thoughtful reply with insight and not a waste of time whine about the price. Too bad it took 30 other posts to get to it.

  18. I still dont see the point of these without a giggle switch. If your going to near pistol size, at least get a useful caliber.

  19. “The goal here was to create the smallest possible platform, while reducing snag points, and maximizing concealability.” LOL, that’s hilarious, but I checked my calendar and it’s not April Fool’s Day.

    “Smallest possible platform” — Are they f–ing kidding?
    it’s 14.5″ long and weighs 4.5 pounds! And yet it has only a 3.5 inch barrel, like a compact pistol, so it’s no more powerful than a compact pistol. By comparison, the Ruger LC9 is only 6″ long and has a 3.12″ barrel.
    If they were going to go for the “smallest possible platform,” it would be 6.4″ long, not 14.5″ long.

    “Concealability”? Again, are they f–ing kidding? Again, it’s 14.5″ long, and 4.5 pounds! What kind of holster could you conceal this monstrosity in? Compared to this Sig Sauer monstrosity, even Dirty Harry’s S&W Model 29 in 44 Magnum is a pocket pistol! There’s nobody on Earth who could conceal a 14.5″ long, 4.5 pound “pistol”, yet its 3.5″ barrel makes it no more powerful than a subcompact pistol you could hide in an IWB holster!

    “Reducing snag points” — why, so that when a giant draws this 4.5 pound anchor from his pocket holster it won’t snag? LOL

    And to make this joke of a gun even more hilarious, they priced it at $1,835.00. Move the decimal point and charge $183.50, and then it might be worth a look, for someone who can’t afford to buy a compact pistol that’s actually concealable or carryable.

  20. I have one, bought it from my LGS right as they were released to the public. I also have a CZ Scorpion, Ruger PC carbine, and quite a few others. I opted for a Vortex SPARC, and I am extremely pleased with the results I get. It’s extremely accurate, reliable, and very compact…..CONSIDERING what it is. My only complaint(s) is/are the “integrated muzzle break”…..and I’m not crazy about the grip, but $20 and that’s a non-issue that hasn’t bothered me enough to change it. I do wish it was threaded, however. I paid $1500, no complaints though overall. It goes to the range almost every time I go. I don’t have very many other firearms that I can say the same about. I am equally pleased with the Scorpion, although I have made modifications to it that I felt were a must. Namely, the safety and mag release. Out of the box, I can’t say that it was as user friendly as the Sig. Mind you, this is all just one man’s opinion and “personal” experience. Take it for what that’s worth….(nothing ??? hahah)


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