Sig MPX Copperhead Review: Fun but worth it?

by Ryan Cleckner

February 11, 2022



SIG Sauer’s MPX Copperhead is the most compact pro-grade sub-caliber carbine available. With its ultra-compact and lightweight design, this little 9mm PDW is easy to carry and a ton of fun to shoot…which leads us nicely into our full SIG MPX Copperhead review!

Sig MPX Specs

  • Host Platform Sig
  • Caliber 9mm
  • Magazines MPX
  • Weight 4.5 lbs
  • Capacity 20 rounds

What is the Sig MPX Copperhead?

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.

Sig MPX Copperhead Features

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 1/2 Inch Barrel

This barrel is designed for maximum deployment in all situations.

Sig Mpx Copperhead Review – Our Take

At 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 its 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).

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 a better target.

At first, we really weren’t sure about the pivoting brace. Up until now, pistol braces were fixed (as far as the rotation goes) and we weren’t sure if the new rotating brace would be a benefit or a hindrance. According to Sig, the pivoting stock adjusts to your arm position so you can take full advantage of Sig-MPX-Copperhead-Pistol Gun Universitysights/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.

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 capable. The Copperhead is a BLAST to shoot and if you’re looking for the smallest 9mm carbine that is also professional-grade, the Sig Copperhead may be for you.

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

Sig MPX Copperhead Review: Pros and Cons

  • Sleek/Lightweight Carbine Design
  • Closed Rotating Bolt Design
  • Collapsable PCB
  • Rugged and Reliable
  • Price
  • Front Hand Stop Concerns
  • Barrel Doesn’t Allow Attachments

Report Card


This is the most reliable 9mm carbine system


Accurate enough


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


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


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


Our Grade


Reviewed by Ryan Cleckner

Reader’s Grade


Based on 14 Reviews

Your Grade

Do You Own This Gun? Leave A Review

Success Your Grade Has Been
Added To Our Reader’s Score

The Sig MPX Copperhead is such a fun gun and well worth getting. If you own it already or are going to, you’re gonna need some key essentials.

Once you’ve got the basic needs down for your MPX Copperhead, time to move on to the fun stuff. How about some upgrades?

Best Sights for the Sig MPX Copperhead

With its relatively short rail space on top, the Copperhead isn’t the best candidate for iron sight – instead, this thing just begs for a red-dot sight.

However, when picking a red dot, you might want to keep it small and low-profile so that it “belongs” on this ultra-compact gun.

This is made by SIG for their firearms, and the ROMEO5 features their MOTAC (Motion Activated Illumination). I love that this extends the life of the battery and activates when movement begins. The ROMEO5 mounts on any platform and is highly durable. CHECK AMAZON PRICE

This company is not as known or popular as other brands, however it is a very good red system. I like that it uses both a solar cell and high capacity battery to power the optic, making sure I always have a reliable point of aim in the field. Thats a big deal for me!

Check amazon Price

Other Guns of its Class to Check Out

The Sig Copperhead is a pretty unique little gun. If you’re into the Copperhead and looking for something similar, check this out:

#1 Flux Defense MP17

Check Latest Price

  • Shootability A
  • Reliability A+
  • Ergonomics B
  • Accuracy A
  • Value A+

Our Grade


Reader’s Grade


Based on 7 Reviews

Your Grade

Do You Own This Gun? Leave A Review

Success Your Grade Has Been
Added To Our Reader’s Score

PDWs are super popular now. It seems like the industry is flooded with 9mm carbines. And why not? They’re a ton of fun to shoot, low recoil, compact/concealable, and they shoot inexpensive ammo. READ MORE HERE

How to Care for Your Sig Sauer MPX Copperhead

To keep your firearm lasting and fully functioning, keep it clean and maintain it. The Sig MPX Copperhead is an outstanding firearm, so it’s important to take care of it. To help you do this, here is a video on breaking it down.

If you’d like to get started cleaning your gun, here is our recommended cleaning kit for the Sig MPX Copperhead:

There is plenty out there on getting “snake bitten” by the MPX Copperhead. We’ve put a few keys things below, to make sure you are aware of them with this firearm:


Click on a star to rate it!

Average rating 4.1 / 5. Vote count: 18

No votes so far! Be the first to rate this post.

About Ryan Cleckner

Ryan is a former special operations sniper (1/75 Ranger) and current firearms attorney, firearms industry executive, university lecturer, and bestselling author of the Long Range Shooting Handbook.

Recent Posts


  1. The Copperhead has a very specific role and does it very well. It’s built as a very compact AR9 pistol that can be packed into “regular looking” small sling bags, laptop bags or backpacks that don’t scream that you have a firearm in the bag. But when you need it can be deployed quickly to put threats down. Just a few years ago one had to separate an AR pistol’s upper and lower just to fit a bag that the Copperhead fully assembled fits into. Most people who want a Copperhead usually already have multiple platforms and are willing to pay the price because of it’s size. It’s not a 100 yard weapon more like 25 yards or closer. It’s built for CQB, fleeing active shooter situations, or where mobility and maneuverability are restricted like a vehicle or room clearing. If you want to suppress it then the MPX-K is better because you aren’t worried about size. But if one wants to go from one location to another and not be noticed as someone with a AR. The Copperhead can definitely fill this role. It’s the best conceal carry PDW because of its size and capabilities.

Leave a Reply

Your email address will not be published. Required fields are marked *