Striking with the ferocity of its namesake, the SIG MPX Copperhead is the most compact pro-grade sub-caliber carbine available.

With its ultra-compact and lightweight design, this pit viper of a weapon is manufactured for maximum performance and minimal snag points to provide the best operator experience possible. Its unique design allows it to be one of the best of its kind for top concealment and quick, easy deployment.

But enough talk, let’s get into our SIG SAUER MPX Copperhead review!

SIG SAUER MPX Copperhead



Reliability: A+
Customization: C
Accuracy: A
Ergonomics: B+
Value: A

Final Grade: A-

MPX Copperhead Origins: The Birth of a Viper

So, how did the Copperhead come to be? There are a few theories surrounding this weapon.

One is that it was custom designed from customer input looking for a lower cost version of SIG’s MPX. And a version that had more features, but didn’t lose the MPX’s closed rotating bolt design.

Another is that the Copperhead was created specifically for the US Army and its Sub Compact Weapon program. Whether that’s entirely true or not is speculation, but the Copperhead has already received numerous government contracts since its debut at the 2019 SHOT Show in Las Vegas.

GUN Specs

Operating System Gas Piston
Caliber 9mm Luger
Weight 4.5 lbs
Twist Rate 1:10
Mag Type MPX

SIG MPX Copperhead Features And Changes

1. Rapid Deploy PCB Brace
When fully extended, this brace rotates to allow the user the ability to contour with the pistol itself.

2. 20 Round Magazine
The Copperhead’s reduced magazine only adds to its conceal ability and deployability.

3. Integrated Flash Hider
With the Copperhead’s integrated flash hider, the crown of the barrel is protected and the overall length is kept short.

4. Ultra-short Integrated 3 and 1/2 Inch Barrel
This barrel is designed for maximum deployment in all situations.

SIG MPX Copperhead – Our Take

Sig MPX CopperheadAt first glance, the MPX Copperhead is a beautifully designed weapon. It really is a head turner with its sleek, yet simple profile and custom Cerakote finish. But don’t let its simplicity fool you. The Copperhead is packed full of awesome and useful features.

SIG continues its trend of putting their customers and clients first with their MPX standard ambidextrous controls. This may seem trivial, but using controls that are natural to your body make all the difference–especially in a high-action scenario. We wish that some of these ambi-controls were on our Sig MCX Rattler (ahem…Sig).

Sig MPX CopperheadBut that’s just for starters. SIG went down to a monolithic upper on the Copperhead (opposed from others in the MPX series) to help reduce its size and weight. SIG designed the Copperhead to be an ideal choice for a “bag gun”, and they did a great job achieving that goal – this thing is TINY.

Although the Copperhead has been swapped to a monolithic upper, that doesn’t mean that you can’t use your fair share of attachments. The Copperhead ships  with a full-length Picatinny rail (as requested by the US Army) making sure that you can utilize any sights or optics devices you choose. There’s also a three slot Picatinny on the rear of the weapon allowing for the use of various sling or stock attachments. And that can definitely come in handy.

One of the nicest features to come with the Copperhead is the collapsable brace integrated into the receiver. The SIG PCB (Pivoting Contour Brace) allows the shooter to really get down on the sights and maneuver around to better target.

At first, we really weren’t sure about the pivoting brace. Up until now, pistol braces were fixed (as far as rotation goes) and we weren’t sure if the new rotating brace would be a benefit or a hinderance.  According to Sig, the pivoting stock adjusts to your arm position so you can take full advantage of sights/optic on the Copperhead. Sig is right. If you’ve ever used a standard pistol brace as it was intended (most people don’t), you’ve likely noticed that the pistol is canted so much that it makes aiming awkward.  Sig’s new rotating brace fixes this and allows for aiming without having to fully straighten nor lock your arm.

One thing that shooters may not find fully pleasurable is the forend (or lack thereof). There is a front hand stop separating your hand from the muzzle, but the with the shortness of the barrel… let’s just say you need to be extra aware of your non-firing hand. (Just like any time we handle firearms. Right folks?)


Now, let’s talk about that barrel. The Copperhead comes standard with a 3 1/2 inch barrel. This is yet another tactic employed by SIG to maintain peak deployability. But there’s one thing about it that I’m not so keen on: the barrel’s flash-hider is permanent with no threads. That means no suppressor or barrel attachments.


This is my only real gripe with the MPX Copperhead. One of the main reasons for a sub-calibered “not-a-rifle” is to be able to shoot with a silencer. If you agree, then the standard Sig MPX might be for you. Or… you can swap the barrel with any other MPX barrel to get the threads you desire.

Although I don’t like it, I do understand where Sig was going with this. The permanent flash hider cuts down on cost and weight while keeping the overall length small enough to fit into a backpack (which would not be possible with a silencer attached).

But how about the weapon as a whole? How does it stand up to serious use?

When it boils down to it… The Copperhead proves itself more than reliable and capable. The Copperhead is a BLAST to shoot and if you’re looking for the smallest 9mm carbine that is also professional-grade, then the Sig Copperhead may be for you.

One final note, I’m a bigger guy (with an even bigger head) and the extreme small size of the Copperhead made it a little difficult to shoot well. I prefer the standard MPX, but that’s only because I’m not looking for the smallest package. If you are, the Copperhead is for you.

SIG SAUER MPX Copperhead Pros and Cons

Sleek and Lightweight Pistol Carbine Design

Closed Rotating Bolt Design

Collapsable PCB

Rugged and Reliable


Front Hand Stop Concerns

Stock Barrel Does Not Allow for Any Attachments

Report card

Reliability This is the most reliable 9mm carbine system


Accuracy Accurate enough


Customization Not much you can change. Fixed flash hider, no mounting options.


Ergonomics Much better ergonomics than other firearms in its class but its small size makes it less ergonomic.


Value Great value for what you’re getting and less expensive than other MPX models


Final Grade: A-

SIG MPX Copperhead vs CZ Scorpion EVO 3 MICRO

Honestly, a better comparison would be the standard Sig MPX to the CZ Scorpion because they are closer in size. The Copperhead, as you know by now, is the smallest possible version of an MPX and therefore has some limitations and/or advantages due to its size alone and not its other features. However, let’s compare:

The Sig MPX platform, and by extension the Copperhead, is a better gun. It has better ergonomics, better controls, better recoil, and I am a BIG fan of the operating mechanism – unlike most 9mm carbines, it isn’t a recoil operated (or delayed) system which I think results in a safer, better recoiling, and more reliable system.

Although the Copperhead is a better (and smaller) gun, it is also more expensive.

The CZ Scorpion is an EXCELLENT firearm for its price. Sure, there are things that could be improved (see the list of pros for the copperhead above), however, that would very likely make it as expensive as the MPX series.

So, if you want an affordable, fun, and reliable 9mm carbine, get the CZ Scorpion. If you want a higher-end pro-grade 9mm carbine and cost is not a limiting factor, get the Sig MPX Copperhead.

Sig MPX Copperhead vs Sig MPX

If you want the smallest possible MPX, get the Copperhead. If you want a 9mm carbine that you can easily suppress, change muzzle devices, have more forend mounting options, or a longer stock to easier shootability, get the standard Sig MPX.

MPX Copperhead Breakdown and Brace Replacement

The MPX Copperhead does have some degree of customization to it albeit not as much as some may want. One of the areas that an owner may want to change is the PCB. Thankfully, SIG makes our lives easier when wanting to do this. The Copperhead is a relatively easy firearm to breakdown and reassemble.


As you can see in the video above, the short barrel on the gun will lead to more frequent cleanings. Be sure to properly maintain your weapon to ensure its reliability.

Our Top Upgrade Picks for the MPX Copperhead

With the MPX Copperhead, there is some definite room for customization. Here are our top picks:

Best Scope/Sights for SIG MPX Copperhead

SIG SAUER Flip Up Iron Sights– The full length Picatinny rail allows for the optics of your preference. But for the Copperhead, I’d stick with SIG’s flip up irons. They’re a good quality set of sights from a name you can trust.

Best Replacement Barrel for SIG MPX Copperhead

4.5 inch MPX Threaded Barrel– This new barrel will give a little bit more of an extension without sacrificing too much of the compactness that the Copperhead is aiming for. Plus, the threads allow you to install a suppressor as you see fit.

Best Replacement Brace for SIG MPX Copperhead

SB Tactical MPX Pistol Stabilizing Brace– For those of you looking for a new brace, this might just be the way to go. SB Tactical nails it with this providing you an adjustable way to maintain your three points of contact.

Best Trigger for SIG MPX Copperhead

Timney Triggers SIG MPX Trigger– The stock trigger on the Copperhead is a MILSPEC-type trigger with a weight of roughly 7.5-8 lbs. Timney Triggers makes an excellent SIG MPX Trigger with a 4.5 lb pull weight.

What lies ahead for the SIG SAUER MPX Copperhead?

The biggest buzz surrounding this weapon is its potential US Army applications. The Army has already stated that they are looking for the next newer, smaller sub machine gun. Is the Copperhead the platform they are looking for?

Check out these two articles for more on this situation: