Review of Sig MPX

A Comprehensive Guide


Review of Sig MPX

Specification Comparison and Reviews

The SIG MPX is a fun and intuitive firearm with features very similar to the AR-15. If you are familiar with the AR-15 platform, the controls will just come naturally. It’s also a very compact gun. The first submachine gun released by SIG SAUER operates on a short-stroke gas piston system and fires from a closed bolt, locked-breech position. Here we will present a detailed Review of Sig MPX.

Table of Contents

The SIG MPX is an innovative firearm that offers excellent versatility. You can use it in CQB scenarios with one more minor receiver piece or configure it for up to three parts, allowing the shooter to have a “rifle” configuration. With the two-piece design, you get quick-to-detach barrels, so you don’t have to unscrew anything or use wrenches if you want to swap out your barrel. Using the three-piece chassis gives you even more modularity since your hands/upper receiver can easily switch between AR-15 and 9mm uppers without any tools.

Features of Sig MPX

The MPX is SIG SAUER’s first entry into the Submachine gun market. It feels just like an AR-15, so all its controls and features translate exceptionally well. If you’re used to the AR-15 platform, it’s a great-looking gun. The stainless steel barrel is easily accessible from the front, doing cleaning and changing barrels. Here we will explore its features in detail.

Magazine Capacity

The SIG MPX comes with two 30 round Magpul magazines in addition to an oversized trigger guard to accommodate gloved hands. Although it is compatible with other 9mm AR-15 magazines, the only ones I’ve seen that work well are Magpul’s PMAG polymer 30 rounders.

Magazine Capacity of Sig MPX


The MPX comes in the right around 7 pounds unloaded and ready to fire. That is a bit much for a CQB gun, but it makes sense considering it has a full-length barrel and its short-stroke gas piston system. It is a lightweight firearm that operates quietly despite being very compact. 


The firearm has excellent potential for customisation since it uses standard AR-15 grips, triggers, buttstocks and handguards. It was designed from the ground up as a modular platform that allows accessories to be added as needed. It is also compatible with Sig’s box magazines and STANAG mags if you want to use it for CQB or switch between 9mm and 5.56/300 BLK much easier since they’re the same size except for calibre.

Customisation Options

Customisations options available for Sig MPX are limitless.

– Collapsible stock

– Vertical foregrip

– Ambidextrous charging handle

– Multiple types of optic mounts

– Back up iron sight (BUIS)

– Adjustable gas system for suppressor use.


Using the Picatinny rails, accessories may be mounted to the front, back, top, bottom and sides of the MPX. Practically any optics or sights can enhance accuracy at range or increase your peripheral vision in close quarters combat situations.

Customisation Options Of Sig MPX


The Sig MPX is an excellent firearm offering a ton of versatility in a small package that you can configure into many different roles without much effort. The controls are very intuitive and feel natural, so target acquisition is simple. Its short-stroke gas piston system has incredibly soft recoil and quickly follows up shots because no bolt/carrier movement is not required to absorb energy. It is also very lightweight, so it doesn’t tire you out as quickly when firing offhand.

Ambidextrous Feature

The ambidextrous safety is also expected and works well for me, but it may not perform as smoothly with people with more giant fingers. The magazine release is located in an odd spot behind the trigger, so it’s a bit challenging to access if you have smaller hands or short fingers. Also, since this gun takes MPX magazines, it would be difficult to insert a fresh magazine into the gun if your hands are full of other things (if you’re reloading/maintaining another firearm). If these features are essential to you, then keep that in mind before purchasing this model.


The gun comes with standard flip-up sights, but they are small and not very bright/easy to see through during the day. The flip-up sights are low-profile and don’t distract from the overall look of the gun. The rear sight is adjustable for windage. There’s not much light-gathering ability on these sights since they’re pretty small. It also comes with backup iron sights should your optics fail or you don’t feel like using them.

Adjustable Gas Piston System

The Sig MPX is the first submachine gun to feature a gas piston system. This operating system works by redirecting combustion gases from each shot through a small tube, reducing the amount of recoil felt on the shooter’s shoulder and significantly improving accuracy. The short-stroke piston design makes it very clean-running, which reduces fouling of the actions over time, increasing its reliability even more. It also makes for very soft recoil and quick follow-up shots since no bolt/carrier movement absorb energy.

Combination Magazine Well Adapter

The SIG MPX comes with two magazine well inserts that allow AR-15 magazines and standard 9mm box magazines. The optional insert is ambidextrous, giving the user more accessible access to their accessory or optic rail on top of the receiver.

Magazine Release

The magazine release is located behind (and somewhat underneath) the trigger, so it’s kind of difficult to reach if you have smaller hands or short fingers. If this is something you care about, keep it in mind before purchasing this model because you cannot change it out like most other AR-15 firearms.

Charging Handle

The MPX was created with a non-reciprocating charging handle on the left side of the upper receiver, which makes it friendly for lefties while still offering ambidextrous controls. The charging handle is non-reciprocating, so it doesn’t get in the way while firing, which is nice. It seems flimsy and wobbly, but I haven’t had any issues with it yet. This chassis does not come with a forwarding assist, so if you think you may need one, keep that in mind before purchasing this model.

Charging Handle of Sig MPX

Safety Selector/Bolt Catch

The safety selector is not ambidextrous, but it’s easy to operate from either side. You can release the bolt stop by placing your hand behind the charging handle and applying pressure towards the chamber. This system is similar to how you would do it on a standard AR-15, so no complaints here.


It has very natural and comfortable in your hand, making target acquisition simple and easy even when firing offhand with its four 3rd generation steel body side-folding (also removable).

Grip of Sig MPX

Action (Slide)

The slide is effortless to pull back even though you can’t get a good grip on it since the part sticks out behind the mag well. I would’ve liked Customisationsome form of texturing or serrations on the slide because that assists in a smooth shooting experience. There is a small light on the side of the gun that turns on when you pull the charging handle back. It’s pretty bright but not blinding.

Bolt Release

There are two bolts included with this model – one for 9mm and one for .357 Sig/40 S&W. The bolts are easy to switch out without any tools since they have holes in them, so you can use an Allen wrench or something similar to push down on the bolt while it’s still in the gun. The bolt release is located within reach of your trigger finger, so if you want to lock your bolt back, it shouldn’t be too difficult, even though there aren’t any serrations here either.


This gun maybe a little more expensive because it’s in high demand, but since SIG is such a well-known company, you get excellent quality and durability at the end of the day. I feel like the price point sits somewhere around $2,000, which can be a bit too expensive for some people. If you’re not willing to dish out the money, then there are other SIG MPX models available that fit your budget!


The safety is ambidextrous and easy to use with either hand (it doesn’t matter which side the safety is on). When applied, a red dot shows up on both sides of the gun, knowing that your firearm won’t fire.

Safety of Sig MPX

Accuracy & Power

The SIG MPX has better accuracy than the AR-15 because of its design and manufacture. It’s made with tighter tolerances, so there isn’t much room for error. It is also one of the reasons why the SIG MPX is more expensive. You can expect greater accuracy at medium distances or about ~200 yards. Since this gun is directed towards people who are into shooting sports like 3-gun, you’ll be able to make tighter shots easily.

Advantages of Sig MPX

– Ambidextrous safety.

– Easy-to-operate slide.

– No tools required to switch out bolts.

– It comes standard with flip-up sights and Picatinny rail (so you don’t need additional purchases if you want accessories like flashlights or sights).

– Price is reasonable for a gun manufactured by such a reputable company.

– Rapid action bolt system.

Disadvantages of Sig MPX

– The magazine release is behind the trigger and close to the grip (which makes it difficult for people with smaller hands to access).

– The bolt release doesn’t have serrations on it, which can make it more challenging to use.

– Requires an Allen wrench for bolt removal (but that’s easy to work around).

Sig MPX Vs AR-15

The SIG MPX is extremely easy to break down and clean compared to an AR-15. You might have some issues getting used to all the small pieces, but It is still convenient to use. The extended rail makes it easier to hold/grasp if you’re using gloves or if your hands are wet/cold, whereas the AR-15 will feel more slippery in comparison. If you enjoy shooting both 9mm and 5.56mm, this system is perfect for you because of its versatility. With one more minor receiver piece, switching between calibres takes less time, which saves time overall.

After Market Accessories - Review of Sig MPX

The MPX was designed from the ground up as a modular platform that allows accessories to be added or switched out if needed. One other great feature is its ability to accept standard AR-15 pistol grips and buttstocks if you wish to upgrade down the road or replace something that broke. There is a lot of potential for customising this gun with standard AR-15 parts because it is built around an AR-15 standard. 

Holsters for Sig MPX 

When it comes to holsters, there is something available for everyone, no matter their standards. Sig has made holster options that fit either side of the receiver from top to bottom and accommodate all optics mounts. Holsters come in left-handed configurations as well. Below are some of the holsters options available for Sig MPX.

IWB (Inside The Waistband) Holsters

These are an excellent choice for concealed carry because they offer full coverage and stability while protecting guns from sweat and body oils during everyday carry. These holsters generally have a low-profile design that hugs the body tightly but doesn’t get in the way when you bend or move around. It ensures that your firearm stays put even under heavy activity.

OWB Holsters

These rigs are great for open carry scenarios where carrying a larger firearm is necessary or if you want to have more options when it comes to concealment. The most beneficial aspect of these holsters is that they offer both safety and quick access to your weapon, so you don’t have to worry about the draw being slow or hampered in any way.

Kydex Holsters

These are inexpensive and work well for duty use, but they tend to wear out pretty quickly if they’re regularly used in training or self-defence scenarios. Kydex holsters are more expensive, but they offer significant advantages when compared to nylon varieties.


One of the most valuable modifications you can make to your Sig MPX is adding an optic. Optics will allow for better accuracy over longer ranges and increase target identification whether you are shooting at targets or hunting games. For this reason, there are multiple options available when it comes to attachable optics, including:

– Sniper scopes

– Holo sights (red dot)

– Back up iron sight (BUIS)


No matter what type of accessory you need for your Sig MPX, something is available to meet your needs.


Yes, It currently has a 1/2×28 thread pitch, so any standard 9mm suppressors will fit onto it.

Yes, the Sig MPX comes equipped with backup iron sight (BUIS) for short-range situations or if your optic becomes damaged or unserviceable.

The most common type of optic includes red dots or holographic sights, which increase target identification and accuracy over longer ranges. For this reason, you can attach sniper scopes to the Sig MPX as well.

Yes, You have two options to choose from if you want to attach an optic: low profile Picatinny rail mounts or integrated optics.

The overall length varies depending on what accessories are attached and which rail system is chosen. On average, it measures about 25″ long.

Gun prices can be different depending on where you purchase them, but they range in price between $1,500 to $5,000.Customisation.


As we’ve reviewed, Sig MPX is a powerful and innovative pistol that deserves serious consideration for your next purchase. If you own or carry a handgun on the job, this may be just what you need to provide some peace of mind when defending yourself in dangerous situations. It also has four steel side folding Sig Brace stocks and backup iron sights should your optics fail, or you don’t want them on there. All those features make the SIG MPX an extremely versatile firearm with loads of potential uses from home defence to competition.


The gun is decently priced for what it offers, but the weight and awkward placement of its controls could be a deal-breaker for some people, so keep that in mind as well. We hope this article has been helpful as we took an in-depth look at the features that make the SIG MPX stand out from other handguns in today’s marketplace.

Author Profile

Gabriel Tackett
Double major in Engineering and Geology at the University of Minnesota. Experienced shooter & hunter for over 15 years. Certified NRA officer for over 10 years working as a writer at .

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