SIG MPX Copperhead 9mm Pistol Review

SIG’s MPX Copperhead is a versatile pistol. (Photo: Levi Sim)

SIG Sauer’s MPX Copperhead is a 9mm pistol. But don’t pigeonhole it with the other handguns you’ve experienced. It’s a versatile firearm that’ll eat any ammo you throw in it and fit almost anywhere you’d like to keep it. It’s big (-ish) for a traditional pistol but tiny for a PCC and it’s got a stock brace to keep you on target. It’s functioned flawlessly and shot accurately with each ammo I’ve poured through it. Let me show you the details and some shooting examples.


The Copperhead is the chopped little sibling of SIG’s MPX group. The barrel is just 3.5 inches long, and the whole frame is just 14.5 inches long. At 2.4 inches wide, it’s probably thicker than most of the pistols in your safe, and its 8-inch height makes it pretty tall, and that’s without a magazine. It weighs 4.5 pounds and you can feel every ounce of it when you add a full 20-round magazine and an optic and try to wield it one-handed. You’re probably not going to be wearing it on your hip.

The Copperhead will be familiar to AR owners.


It’s got a monolithic upper–it’s all one piece of aluminum. While its controls are completely familiar to AR users, it’s more streamlined than most AR’s. There’s no dust cover, there’s no handguard, there’s nothing extra to snag or get caught up when deploying from a concealed location. You can hold it pretty much anywhere with your second hand and get a solid grip.

The front of the mag well is the natural spot for your second hand to grip the gun. It’s checkered for a positive grip.

The pistol grip looks small, but it’s very ergonomic. Several people I’ve shared it with have commented that they’d love to put this grip on their AR’s. It’s narrow at the top and flared at the bottom in three dimensions so it fills your hand well, and it seems to fit small hands and large hands equally well.

The grip is smaller than many other AR-style grips, but it fits both and small and large hands well. The flared base forces your hand upward and the texture makes a sure grip. Even gloved hands fit inside the trigger guard.

The over-sized mag well guides magazines into place and is a good spot for a second hand to grip. The frame extends out under the barrel and flares downward to keep you from gripping too far forward and getting in front of the barrel. It’s very intuitive to hold and I never felt my hand was in danger of mistakenly wandering downrange.

We’ll talk about the wrist brace below.

Although the styling is a little blocky, the Copperhead’s looks grow on you in direct proportion to how much you shoot it. After several hundred rounds, I think it’s gorgeous. SIG’s Romeo5 red dot is not included with purchase.

The first time I saw it, I thought the Copperhead looked like something from the Soviet era–like the Yugo car company made a sub-machine gun. The upper and lower receivers are Cerakote finished in flat dark earth, and they dwarf the diminutive black pistol grip and the skinny 9mm magazine. However, the more you shoot it the better it looks. Now I recognize that the simplicity of the exterior allows it to deploy smoothly. The action works as simply and as flawlessly as the exterior. I’ve changed my mind and I think it’s a good looking gun.


The Copperhead employes a short-stroke gas piston. This system allows it to shoot all kinds of weights and charges of ammo without making any adjustments to the gas valve. I pulled it out of the box and shot Winchester white box 115gr, cheap Norinco rounds, Winchester USA Forged steel case 115gr, Winchester Train and Defend 147gr (Train), Winchester USA Ready 115gr, and SIG’s M17 Military Grade 124gr which is a +P military grade ammo. Everything cycled flawlessly and all the casings ended up in the same pile. There’s nothing to report about recoil–the bolt carrier’s mass takes up most of it. It stays on target well.

The Copperhead cycled flawlessly and shot accurately with everything from mystery weight Chinese rounds, to 115gr, to 125gr +P, to 147gr.

Some of this consistency and reliability comes from its fully-closed and locked rotating bolt. It locks up tightly and the breach doesn’t open until the charge is well spent and the pressures have passed down the barrel. The carrier moves back and the breach begins to open, but the bolt remains locked to the chamber. Plus, there’s a lot of frame material. It’s a safe system and there’s no ill-effect from gases coming back at the operator. The bolt’s rearward travel is stopped by a hard rubber bumper, not a spring-loaded buffer tube like on an AR.

The bolt carrier group. The top is struck by the short-stroke piston and driven rearward. The two springs push it back forward to finish the cycle and load the next round.
The bolt locks fully and has a rotating face.
The bolt face will lock forward into the chamber and then be completely covered by the rest of the bolt carrier, which is also overlapped with frame material from the outside. There’s a lot of material to protect the user.
This is the view down the frame with the bolt carrier group removed. You can see the lugs where the bolt locks in. The barrel is on the right, the scope is in my hand on the left.
The bolt’s rearward travel is arrested by this hard rubber bumper, not a buffer tube.
This is looking from down the barrel from the front with the bolt carrier group removed.


Fully- and truly-ambidextrous is the way to describe these controls. Everything is laid out similarly to an AR rifle. The magazine release and bolt release buttons function from either side in exactly the right position. The selective-fire/safety switch is right above the grip and is exactly the same on either side. The charging handle is typical AR-style with release latches under both wings. The brace release button is on the right side, but it’s only used for collapsing the brace.

The safety switch, bolt release, and magazine release are fully ambidextrous.

Spent casings are sent out the right side of the weapon, but they fly forward so even left-eyed shooters with it pressed to the shoulder won’t be eating brass.

The AR-style charging handle has ambidextrous latches.

The trigger is not a cheap mil-spec job. It’s polished and nitrite coated. It’s smooth with a short takeup. The takeup is also smooth and consistent. After it fires, it’s got a solid back wall and short reset.

The trigger is smooth and consistent with a short take-up and solid back wall.

You can upgrade the trigger to a special Timney trigger developed especially for the MPX line and it is reportedly very good. You may be able to swap it for a drop-in AR trigger, but the trigger may be ruined by the gun. The triggers used here have a special block that keeps the trigger from wearing out prematurely. Having said that, I’ve read plenty of forums where certain standard AR triggers have lasted normally in MPX guns. Caveat Emptor.

There’s a block at the back of the trigger assembly that protects from heavy abuse. Typical AR triggers lack this block and may not last well. But Timney has created an MPX-specific trigger that is a good upgrade. The front of the gun is to the right.



No sights are included. There’s a full-length Picatinny rail on top and I used SIG’s Romeo5 red dot, which is ideal with this gun. It comes up naturally either with arms extended or with the brace and you’ll find targets quickly. Pop-up iron sights would be more concealable and should also work well in normal lighting. There are about 8 inches of mountable space on top of the rail. Could they have included sights? Sure, but this way keeps the cost down and you can add exactly the sight you want.

The Copperhead doesn’t include any sights, but it’s got a full-length Pic rail so you can customize as you wish.

Stock Brace

This is a pistol, not a rifle, not an NFA item, so it doesn’t have a shoulder stock. It does have an articulating brace that fits on your forearm. Fortunately, it locks completely open so you can “brace it” against your body, which is a terrific way to work with this gun. With the brace, I was making tight groups even with rapid-fire. The sights sit high and if you get your jaw against the bars on the brace your eye will fall right in line.

The only control that isn’t on both sides of the gun is the button to collapse the brace; it’s only on the right.

The brace is effective at stabilizing the gun when you use a two-handed grip with your arms extended. Using your second hand, you can pull against the brace and get a stable grip that keeps the sights on target. You can also use the brace with a one-handed grip and it’s certainly steadier than without.

This is using it two-handed with the brace on the forearm. It’s cumbersome to get in and out of the brace, but at the range, it definitely improves stability.

The brace is effective, but it’s clearly designed within the limits of the law.

You can always register it with the ATF as an SBR, then get a folding stock and mount it to the tiny Pic rail at the back of the frame.


The Copperhead takes the standard MPX barrels, so you could swap the 3.5-inch barrel for the longer K barrel that is threaded for a suppressor. Since the barrel doesn’t move, you won’t need a Nielsen device. The 3.5-inch barrel includes an integrated flash hider.

The barrel is just 3.5 inches long with an integrated flash hider, but it can be swapped with other MPX barrels, like the threaded K barrel.


It ships with one 20-round mag, but there are also 30-round mags available. These are interchangeable with SIG’s other MPX guns.

One 20-round magazine is included, but it’s compatible with 30-round MPX mags. A 10-round mag is standard for California orders.


I dare you to shoot just one round. This gun is fun to shoot and using the brace against your body gives you the feeling of shooting an AR without the impact of the rifle rounds. The light recoil makes you feel like a better shooter because it stays on target so well.

Using the brace, there’s virtually no recoil. Even SIG’s M17 +P Military Grade ammo in 125gr is easy to shoot all day.

And it’s remarkably accurate. This gun certainly shoots better than I do. The huge desert crickets crossing the range were easy prey at 15 and 20 yards.

It shoots all kinds of ammo from 115 gr to 125 gr +P to who-knows-what-grain from the mystery bag of random ammo. Everything cycled well even though I wasn’t the first tester to get my hands on this gun. It has clearly been used quite a bit, and I’ve added nearly a thousand rounds to its resume.

My astigmatism makes using a red dot a little imprecise because the reticle sparks larger than normal in my view. At 50 yards, my eye isn’t reliable, so I shot these at 25 yards so I could see the target better. Remember, the barrel on this gun is just 3.5″ long.

25 yards with custom loaded RMR 125gr flat nose bullets. disregard the bottom left holes. 1″ squares.
25 yards with Winchester’s USA READY flat nose 115 gr. 1″ squares.
25 yards with SIG’s M17 +P 125 gr. 1″ increments.

I bet you’ll use it most often as if it’s a carbine with the brace against your shoulder. But, you can also extend your arms and use it with a thumbs-forward grip, and even be accurate with a one-handed grip. That makes it a lot more versatile than a PCC.


I don’t like the safety switch positioning. You naturally grip this gun high, which puts the switch in a good spot for switching to Fire with your thumb. But, once it’s switched, it’s sitting right under your thumbs vertically when you use a two-handed thumbs-forward grip. It’s uncomfortable but doesn’t inhibit shooting. Because it’s under my grip while in Fire, it’s not simple to switch back to Safe. I have to use my second thumb to push it back to Safe, but even then my strong hand’s index finger is in the way. It goes into Fire quickly, which is important in a defensive situation, but for all other times, I’d like it to go back to Safe easier.

Slomo with two hands using SIG’s M17 +P 125gr ammo.

I don’t love the brace. I’d rather have a folding brace that makes the overall length shorter. It’s intended to be strapped on, but it’s only useful that way at the range. I don’t like that it’s intended design is meeting the letter of the law. Still, the brace is useful and it deploys quickly.

It’s kinda heavy, which may be a necessary by-product of being well-built. It looks like it can be dropped in the mud and still keep ticking, but it’s over-built for normal use. Then again, it’s about the same weight as a Desert Eagle.

Two-handed in slomo with Winchester’s 115gr USA Ready flat-nose FMJ ammo.

Who Is This Gun For?

The rumor is that this gun was developed originally in response to a US Military call for proposals. If that’s true, it’s supposed to have been intended for use by protective details–the kind of people who may have to shoot from inside a vehicle, in tight quarters, or keep the gun mostly concealed.

As a handgun it’s huge, but for a pistol caliber carbine, it’s highly concealable. It might even double the value of the car you conceal it in.

If you think of it as a pistol caliber carbine, it is extremely compact. It’ll fit in the center console of many trucks, in the door of a vehicle, and probably even in some glove boxes. It’ll fit next to your 15″ laptop in a bag. I don’t think there are any OWB holsters for it, but I really wouldn’t be surprised. With school teachers being trained for active shooter situations, is this a good option for them?

The Copperhead with an optic mounted fits within the footprint of my 15″ laptop. It truly fits within any bag you’re likely to be carrying.

Is This Gun For You?

The MSRP for the MPX Copperhead is $1,599, but you’ll see it for a little less on the street. That’s a lot for a gun and a lot for a pistol. However, it is a quality firearm. It is built to last, and I suspect the used prices will reflect its value for a long time. It’ll shoot even the cheapest ammo without issues.

Need it to get smaller? Copperhead breaks down without tools in the typical AR manner.

If you want a gun that would be good in a situation, this could be it. It’s highly concealable but ready to shoot. You can adapt it to your needs, but it’s a performer right out of the box. It’s a lot of money, but I think it’s appropriately priced. It’d do well in an emergency and it’s enjoyable at the range. Plus it’s just cool.


  • Pistol
  • Operating system: gas piston
  • Caliber: 9mm Luger
  • Overall length: 14.5″
  • Overall width: 2.4″
  • Height: 8″
  • Barrel length: 3.5″
  • Weight: 4.5 lb.
  • Twist rate: 1:10
  • Magazine type: MPX (10, 20, 30-rnd available)
  • MSRP: $1,599

About the author: Levi Sim is an avid hunter, and an increasingly avid shooter. He strives to make delicious and simple recipes from the game he kills. He makes a living as a professional photographer, writer, and photography instructor. Check out his work and he’d love to connect on Instagram: @outdoorslevi

{ 11 comments… add one }
  • Bad Penguin August 23, 2019, 10:27 am

    I have to say that I am clueless as to why people buy these weapons if they are not full auto. At 4.5 lbs they are 3 lbs shy of an AR-15 rifle and are just about as bulky in close quarters (my opinion) and they offer zero increase in firepower and concealablity is zero.

    • Big Bear December 30, 2019, 8:51 am

      Well, like the article says, it was probably made for a patrol ops first bid proto. But like shoes, and cars/motorcycles/women if you like variety and can afford it, go for it. Since you arent going to use it in a defense situation, like anything else its a good toy for adults

  • Mr Shifter August 12, 2019, 7:00 pm

    Just purchased…..haven’t shot yet. It sure is a fine weapon as far as build quality. Was looking for the CZ Scorpion Micro actually, but came across the Copperhead for the suggested price of $1600.00 locally. Good luck finding one any lower, but I hope you do. It is more money than I have ever spent on a weapon, but I wanted it and I wanted it now. There are a few parts for sure when you tear it down to clean and lube, but wasn’t any harder than an AR-15 (I’m an AK guy). A set of iron sights and an extra mag would have been nice. I bought a 30rd mag and it was expensive….well, to me it was…$64.00….I will make it to the range real soon….and I might as well tell ya’ll, I bought the CZ and just received today and it’s very nice also…..Actually….it feels better (to me) when shouldered, breaks down easier (one pin) and only has three parts total when field stripped for cleaning. Its a couple of inches longer, nice brace, comes with really nice iron sights, and the 30rd mags are only $24.00…..I like them both for sure, but me, without shooting yet, I lean towards the CZ…the looks, body fit ,feel and easier breakdown I just like more. Oh, and the price, was $1,179.00….that in comparison is much better. Actually if the CZ was available when I wanted it I wouldn’t have purchased the Copperhead. The big test is coming up soon, and let me tell you, I’m stoked….Range Day!!!! All in all, either one you pick is a great weapon……..One thing before I close……You would think you would get a hard case with the amount of money these cost…..nope, cardboard. By the way, great write up and photo’s….thumbs up!!

  • Thomas Pilon August 12, 2019, 2:46 pm

    That Romeo adds way too much height. I’d definitely prefer a mini reflex, like a Fastfire III, on a Copperhead. It would be more in line with the compactness theme and given that it would be much closer to the barrel, It wouldn’t need as much adjustment for elevation at various ranges.

  • mike August 12, 2019, 9:56 am

    I love Pistol Caliber Carbines. I own one in 9mm &40S&W. I always wanted an UZI 9mm , but they are so expensive. These may be an option……………IF the prices come down some?

  • Mike in a Truck August 12, 2019, 9:44 am

    This just might be the right thing to conceal ( w/permit) while strolling through the mall. In light of recent happenings what once would have been considered ridiculous now seems like common sense. My how much we have changed.

    • Mike Mapp August 12, 2019, 10:24 am

      I don’t know about the Mall but good luck doing that ☺

    • Beachhawk August 12, 2019, 6:56 pm

      Mall? Who goes to a mall these days? But that is one cool pistol! I might have to buy one just because it’s so cool.

    • dylan August 13, 2019, 5:31 pm

      1. who goes to the mall?
      2. Who is this paranoid? just carry like a normal person and train properly and you wont need a gun like this.

  • Darrell Minix August 12, 2019, 9:18 am

    It’s nice love it a bit pricey

  • Ross S. Riley August 12, 2019, 7:40 am

    Beautiful! The Broom Handle Mauser of it’s day!

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