Sig MPX Copperhead Review

The Sig MPX Copperhead is a 9mm Pistol Caliber Carbine that made by Sig Sauer. This is our review of this interesting firearm.

The Sig Sauer MPX Copperhead is one of the latest pistol caliber carbines (PCC) to come on the scene. While the Sig MPX Copperhead is on the upper end of the price spectrum of the PCC Market, there is a noticeable reason for that price, and it’s not just the Sig Sauer name.

The Sig Copperhead brings an extremely compact 9mm to the pistol caliber carbine market.

The Copperhead was initially released in FDE with a blunderbuss prong muzzle device built into the 3.5-inch barrel.

We’re reviewing the updated version with an A2 muzzle brake and a black finish.

This Cooperhead has the same brace configuration. However, this model is black and comes with a 4.5-inch barrel and an A2-style flash hider.

It ditches the original Tan color of the Sig Copperhead as well as the blunderbuss muzzle device.

Sig MPX Copperhead Features


The Sig MPX Copperhead has an improved AR-15 style ambidextrous safety that’s super easy to disengage and re-engage.

The right side safety is shorter than the left so that it won’t rub on the knuckle or palm of your hand. Sig did a great job making a superior AR-15 style safety that fits the gun perfectly.

Sig Copperhead Trigger


The MPX trigger has a slight bit of creep, then a nice short and light rolling break with a soft but positive reset.

It’s a good trigger for a stock gun, especially in a PDW format like the Copperhead, where a match trigger isn’t needed. But if you’re a trigger snob like I normally am, you can always upgrade to the Geissele Sig MPX SSA trigger or the Timney Sig MPX trigger.

Are these triggers needed on a gun you’re most likely to be used within 25 yards?

No, but they are likely to increase your split times, which means more rounds on target in a shorter amount of time. That said, we had no problem getting sub .2 second splits with the stock trigger.

Honestly, this is one of the best non-match grade stock triggers I’ve ever felt in an AR15 style rifle.

Pistol Grip

It has an AR15 compatible pistol grip, so your options are infinite. But this one is short and compact like the rest of the gun.

Personally, I don’t care for the look. I’ll probably replace it with something like the Magpul K grip that’ll still be nice and compact but won’t look as animated as the Sig MPX Copperhead’s stock grip.

Bolt Release/Hold Open

MPX Copperhead Bolt Hold Open

The Sig MPX Copperhead’s bolt release is ambidextrous but can only be used as a bolt hold open on the left side like a standard AR15. The small textured section used to hold open the bolt is hard to reach due to the left side mag release extending further. The real benefit is the ambidextrous bolt release.

As a right-handed shooter who shoots a variety of guns and has a lot of time behind AR15s, I don’t find myself using the right-hand side bolt release even though it can be faster.

If you’re not regularly training around the Sig Copperhead’s right side bolt release, it’s not easy to drop the bolt. It’s one thing where you have to press it just right because it’s fairly narrow and recessed into the receiver.

If the Sig MPX were the only platform I was using, I would definitely start using it regularly. But since it’s not, I’ll use my left-hand thumb to activate the AR15 style release that I’m intimately familiar with.

Magazine Release

It has ambidextrous mag releases that are easy to reach with either hand and are still low profile, remaining true to the copperhead’s PDW design.  As long as the gun is pointed straight up, the magazines drop free using both the right and left side release.

For most people, it’s easy to reach, but if you have small hands, it might be a stretch.

Magazine Well

The mag well is beveled for easy insertion of the single 20 round magazine included with the gun. Of course, it’d be nice if the gun came with another magazine, but the 20 round magazine really is the best option for the Copperhead variant of the MPX if you’re using it as a PDW.

It’ll accept 30 round magazines as well, but in my opinion, they’re too bulky if you’re running the Copperhead as designed. Keep a 30 round mag in a G Code Scorpion Tall Pistol Mag Pouch or an HSGI TACO for a reload, but I wouldn’t run it as your primary.

Lancer and bombproof make the magazines themselves, but that comes at a literal cost. Magazines for the Sig MPX run $59 plus, so if you’re the type of guy who has to have 10-20 magazines for your Copperhead, you’ll need to take that into account.

Charging handle

The Sig MPX Copperhead has an ambi AR15 style charging handle. The ambi feature is well done but nothing exceptional.

If you’re looking to upgrade your Sig MPX Copperhead, Geissele makes a Sig MPX version of their Super Ambidextrous Charging Handle that’ll fit the Sig Copperhead. But this isn’t going to be an item you’re using a lot on this gun, so it’s probably the last item I’d upgrade.


Really the lack-thereof. The MPX Copperhead doesn’t come with iron sights or any type of optic. I put the Sig Romeo 5 on it, and it works like a dream. I think for the price point Sig could have included some type of optic or sight out of the box.

Granted, I would want some type of small red dot sight over irons, given how short this gun is. However, with a set of Magpul MBUS Pros running roughly the cost of the Sig Romeo 5, it would have been nice if the gun just came with a Romeo 5.

You will want an optic riser on the optic, though, so you can comfortably pick up the dot.  

Pistol Brace

The brace on the Sig MPX Copperhead is extremely compact and quick, and easy to deploy. There is also enough friction on the bars of the brace that it’ll hold the weight of the gun.

Granted, this gun is used but hasn’t had the brace collapsed and pulled enough to wear the finish down. I suspect once the finish has worn down on the rails, it’ll no longer hold its own weight.

To collapse the brace, you press a button located on the right side of the gun near the base of the brace. The MPX is really easy to stow in a discreet case, satchel, or briefcase.

This model saves a lot of space by machining the rail mounts into the lower receiver, so you have a really compact little package.

Considering the overall size of the original Sig MPX this is extremely noticeable.

For a true PDW, but it could have a longer length of pull for plinking on the range, and the brace portion could be less flimsy and not rotate 360 degrees.

If you want to remove the brace, you can replace it with the SB tactical M1913 folding brace. Sig also has a similar version of the brace they use on Sig MPX K and the Sig MCX Rattler.

Mounting Accessories

The standard Sig MPX K has a removable handguard that you can replace with a longer one. The longer handguard fits over suppressors and will give you more reach on the gun.

I’ve got a Lancer Systems Sig MPX Carbon Fiber Handguard on the 8inch MPX. But it would be perfect with a 4.5-inch barrel and suppressor underneath it.

To maximize size efficiency, the Copperhead variants use a one-piece upper receiver/handguard.

With its really short monolithic handguard/receiver the Sig MPX copperhead isn’t the best gun to mount accessories to.

The black Sig Copperhead has an M-Lok mounting slot on both the rail’s right and left sides. The tan MPX Copperhead version does not have these mounting slots.

This isn’t a gun that needs a lot of accessories. This is a gun that, in my opinion, you want to keep as bare as possible.  

Just add a good optic like a Trijicon MRO, Aimpoint T2, or the Sig Romeo 5, and call it a day.

If you want something even lower profile, a Trijicon RMR on a Scalerworks mount or the Sig Romeo03 would make great options.

I wouldn’t add something as big as an EoTech XPS3 or Sig Romeo 8 on this PDW. That said, if you do have to add a light, I would go with something like the Surefire X300 or Streamlight TLR1 and mount it as far forward as possible on the 1913 rail.  


The Sig MPX Copperhead’s short-stroke piston rotating bolt operating system practically makes recoil disappear. The operating system does nothing to the conclusion the 9mm sub-gun clone creates.

You read that right, this wimpy 9mm with 4.5-inch barrel has a lot of concussion on the shooter.

When shooting your normal handgun, your arms extend the muzzle further away from your face, so you really don’t notice the concussion.

If you’ve ever shot close in live-fire weapons retention drills as Craig Douglas teaches in his ShivWorks ECQC.

Personally, I think that’s a result of the A2 flash hider on the front of the gun directing the gasses to the side vs forward of the shooter.

As a 6’ tall shooter, this gun is not easy to get a good grip with my support hand. I’m not a fan of grabbing the mag well, but that technique might make more sense for me on this gun.

It’s still something I’m working through. If this gun were an SBR, I’d most definitely add a VFG (Vertical Foregrip) or AFG (Angled Foregrip) to the front.

It wouldn’t look the best, but it would really allow you to Control the Copperhead when shooting long strings of fire. That said, if there is any gun that you don’t need to work hard to control, it’s the Sig MPX Copperhead. 

This is the gun your friends will ask you to bring to the range every time. But after they’ve shot a mag through it, they’ll put it back in your gun case.

For that range session, you can be sure you’ll be texting or calling you the night before the next range trip asking you to bring the Sig Copperhead.


The Copperhead is an overall attractive looking gun minus the pistol grip which is a practical size but just looks a little small on the larger Sig MPX receivers. The vent cuts on the front of the handguard and the built-in handstop look natural on the short gun.

The largest and most out-of-place feature is the mag well. But it does help with reloads and doesn’t affect the overall size of the gun when it comes to covert storage.

This is a very short gun that was originally proportioned around an 8-inch barrel, so the visuals are a bit off. But it’s a PDW, not a medium-sized sub-gun like the regular MPX or an HK MP5.


The Sig MPX Copperhead comes in at a hefty MSRP of $1878.00 and street price is normally $100-$200 less, so it’s not an inexpensive gun. All you’ll have to do is add an optic and start shooting.

Unlike other options such as the CZ Scorpion, you don’t have to immediately start switching out parts to get the gun to an acceptable baseline for a usable defensive firearm. 

There are aftermarket accessories if you really want to make it your own but they really aren’t necessary.

The biggest downside for me, as a person who likes to have lots of magazines for their firearms, is that the Sig Lancer Mags Run $60 and are impossible to find for less than that.  

Everyone has a different definition of value with some being able to buy a $1900 gun every month and others saving years for that privilege.

If you’re saving years to buy this gun, I’d make sure the PDW format is exactly what you’re looking for.

Unless you really need the PDW format, the Sig MPX K 4.5 is probably the better gun to spend your money on due to the increased versatility. If you’re buying the gun to shoot a lot or suppress it, the MPX K will be more versatile and enjoyable to shoot.  

But if you’re going to use the Sig Copperhead as a PDW, or you really want to have a fun toy for show and tell, then there really isn’t a better option in this price range. It’s extremely controllable for its size, but that concussion takes out the fun factor in the first magazine.

MPX K vs Copperhead

When you’re deciding Sig MPX K vs Copperhead you really have to decide what you want the gun to do. If you plan to suppress your MPX then the Sig MPX K is the way to go.

It doesn’t require an adapter to mount the suppressor, and you can get handguards over the suppressor. You can’t even mount a suppressor to the FDE copperhead due to the blunderbuss style muzzle brake built into the barrel.

Lancer Systems, Midwest, and Sig all make 8-inch handguards so you can extend your grip while covering most of the suppressor.

The length of the brace on the MPX K is also slightly longer and will be a lot more comfortable to shoot as it gets your face further away from the concussion.

If you plan on using the gun for anything but a concealed PDW the MPX K is the better option. It’s more comfortable to shoot and more modular while not being much bigger.

Sig Sauer MPX Pistol

Both the Sig MPX and the SIG MPX K come with a pistol stabilizing brace, making them both pistols. Sig also makes an MPX PCC which is a 16″ barrel version of the Copperhead and the MPX K.

The MPX Copperhead pistol and the MPX K pistol use the ATF approved SB Tactical brace. If I’m not mistaken they use the same brace system on both platforms.

Copperhead Range Cases & Carry

Carrying the MCX Copperhead is slightly different from your typical PCC, the PSA AKV or SBR, like the Honey Badger Pistol, due to its overall length being much shorter.

While there are many case options for the Copperhead, it may best fitfully extend into an SBR case such as The Bureau.

We may make a suitcase-style carrying case for the Copperhead in the future. But for now, the Bureau would be the best option from Lynx Defense.

I’ve also found the Copperhead fits really well in our multiple handgun bag, The Concord. With its modular design, you can easily move inserts around to fit the Copperhead in the bag.

We recently developed a submachine gun rifle case that works with the Sig Copperhead perfectly!

Sig MCX Copperhead Final Thoughts

If you’re looking for a fun range toy that you can comfortably shoot all day long, this probably isn’t the right gun for you.

If you are looking for something you can bring to your local indoor range and shoot a box of ammo, this may be the right gun for you.

It’s hard to accessorize beyond adding an optic, and it’s not a ton of fun to shoot all day.

If you want a gun that keeps in a briefcase or backpack, this is the perfect gun.

The Copperhead is one of the coolest guns you can get for show and tell.

This isn’t the only Sig we have reviewed. We recently looked at the Sig P938 pistol, so if you are in the market for a small 1911 pistol, checkout or Sig P938 Review.

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  1. Nice overview of the Sig.

  2. This barrel is better than the 3.5 inch. I’d replace the flash hider with a KAK can.

  3. Over/Under on the ATF coming after this next?
    6 months?

  4. I really like the PDW”s for a SHTF option, my only suggestion would be to pick one up that uses the same mags as you handgun unless your rocking a revolver.

  5. I could tuck this away in my bug out bag easily… Thanks for the review.

  6. Very nice Sig. I would definitely like to be able to own one

  7. great all encompassing information. Thank you!

  8. Good review on a sweet little setup.

  9. Nice looking gun! Would look really good in my cabinet next to the other guns in my small collection!

  10. Douglas Allen Hunter
    Douglas Allen Hunter

    I think it is a beautiful piece of workmanship,very easy on the eye and boy would I like to own one!

  11. thethinkingmetalhead

    Very sexy, but too pricy for me at the moment

  12. It is a great looking gun and I would love to own one, but for the price I think I can do better elsewhere.

  13. Looks good at least for the states that your allowed to own them in glad I am in Oh.

  14. Great review, tons of information.

  15. I like Sig and their innovations, just not the price

  16. The sig mpx is Definitely on my wish list. Great review.

  17. Samantha Thibodeau
    Samantha Thibodeau

    Anyone Know If This Is Legal To Own In Maine? I’m New To The World Of Firearms, But I Plan On Buying A Few Guns In The Coming Year. Being New To Gun Ownership, I Think The Responsible Thing Is To Be As Knowledgeable As Possible!

  18. Sig keeps pushing the envelope on a continuous upgrade of their products.

  19. Well written review by SIG!!

  20. To start, this was a great review, with nice visuals of the MPX, it has so many variations currently, and the fact that it takes a portion of AR15 parts, that means you can put a ton different

  21. Well Engineered and Compact.

  22. You can’t argue with the quality of Sig. I’m shopping for one now.

  23. I could use one of these. Would be A nice compliment to my Springfield 3.3 S&W 40.

  24. Sig MCX Copperhead – Great PDW

  25. Your reviews are very straightforward and easy to follow. This looks awesome.

  26. BecomingMinnesotan

    Nice! Really looking at a PCC as a next purchase. This one may be a little out of my budget (or a lot!) :).

  27. Always love a nice sig this would be fun to have.

  28. SIG makes a fine product and the MPX is a useful size, but the ATF is itching to hassel people over the “brace”. It’s GTG now but that may change.

  29. Man nice setup. Fast easy and powerful

  30. Paul A. TeNyenhuis
    Paul A. TeNyenhuis

    I like the overall look, I would need to try it out before making any judgements on upgrades.

  31. Nice overview. Hopefully someone will start making cheaper mags.

  32. That Sig MPX Copperhead looks pretty good to me.

  33. I can’t wait until I get a chance to try out a pcc. I’m a firearms enthusiast that enjoys all ranges of calibers and platforms. Thnx for the review

  34. Great! As if my wallet hasn’t been beaten up enough by gun purchases. Now I want this. 🙂

  35. I like Sig’s and I really like this, but because of market conditions and everything else going on. It’s too rich for my blood right now. Would love to have one at some point.

  36. I need one of these now.

  37. I love my Copperhead! I had my buddy Cerakote it with a Copperhead snake skin pattern and it looks amazing. Wasn’t a fan of the A2 so a threw a Lantac Dragon on it.

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