SIG MPX Copperhead 9mm Pistol Review

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.

Sizing

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.

Construction

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 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 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.

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.

Action

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.

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.

Controls

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.

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 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.

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.

Accessories

Sights

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.

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 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.

Barrels

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.

Magazines

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

Shootability

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.

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.

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.

Cons

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.

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?

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.

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.

Specs

• 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