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Sig MPX Review

The SIG Sauer MPX was designed to be a replacement for the Heckler & Koch MP5. The HK MP5 had ruled the sub-gun world for years and SIG decided they wanted to upset that system. To do so, they had to design a gun that was more controllable, cheaper, and just overall better than the MP5. In some regards, I think they did a pretty good job. We’ll cover these improvements in our Sig MPX Review.

Sig MPX Collapsed Brace Right

My SIG MPX review is going to cover what SIG has done right with the MPX and what it has done wrong.

They’ve done a lot of things very well, but the gun is far from perfect.

What is the appeal of the gun?

The SIG MPX feels just like an AR-15, so all its controls and features translate extremely well. If you’re used to the AR-15 platform, it’s a great-looking gun.

If you’re into tactical-style firearms, or you love movie guns, you’re going to love the SIG MPX, which has been featured in a lot of awesome movies.

I know that played a large role in my buying the gun, but since then it has become one of my favorites beyond its screen appeal.


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Sig MPX Long Safety Lever

The safety on the SIG MPX is ambidextrous and essentially an AR-15 lookalike. The right-side lever is slightly shorter so it doesn’t rub your knuckle wrong when you take the safety on and off.

However, the lever is still long enough that I can use my trigger finger to re-engage the safety as opposed to the thumb like you’d have to do with a standard mil-spec AR-15.

Sig MPX Long Safety Lever

Overall, SIG did a great job designing this firearm. It’s about what you would expect at a gun at this price point.

It could be improved upon a little bit if it mimicked something closer to a Radian-style safety, but it still beats a mil-spec variant by a long shot.

Pistol grip

Sig MPX Pistol Grip

The pistol grip on the SIG MPX is a standard AR-15-style pistol grip and it looks like SIG basically copied the Magpul MOE.

For some reason, they went with the standard grip angle that they used on the M16A2, and, in my opinion, they should have used something with a much steeper/more vertical angle.

I would have liked to have seen something that closely mimics the Magpul K than the grip they decided to use, but that’s something I’ll likely switch out as soon as I can find one in stock.


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Mag Releases

Sig MPX Magazine Release

The magazine release on this gun, again, is a standard AR-15 magazine release on the right-hand side of the gun.

However, on the left side of the gun, it’s actually ambidextrous. It’s also well-positioned in the same place it would be for a right-handed user.

It’s easy to use in a variety of configurations.

If you had to strip a magazine from the gun, you can easily press your thumb in on the magazine release and rip it out. (I don’t see why you would do that when you can just press it with your firing hand finger, but either way you have lots of options.)

Sig MPX Ambi Magazine Release

Magazine Well

Sig MPX Magazine Well

The magazine well on the SIG Sauer MPX is actually fairly exceptional with a nice steep bevel inside it, so it’s very quick to get your magazines up into the gun and locked in.

Bolt Release/Hold-Open

Sig MPX Ambi Bolt Release

This gun gets a little more complicated when you start talking about the bolt release.

On the left-hand side of the gun, it has an AR-15-style ping-pong release.

The upside of this is that it does have a little bit of a lever that extends down on the bottom of that release so you can easily lock the bolt back.

It also has an ambi release on the right-hand side, but it’s only a bolt release and does not function as a bolt hold-open. 

Sig MPX Bolt Release

I do wish they had some sort of bolt hold-open feature on the right-hand side of the gun that would make it easier for right-handed shooters.

If you’re a lefty, you might actually find this gun easier to use than your right-handed counterparts.

I generally tend to run this gun with this same manual of arms that I would use with an AR-15 and don’t take advantage of the ambidextrous magazine release or bolt lock.

Charging handle

Sig MPX charging Handle Top

The charging handle itself is, again, in the style of an AR-15.

It has ambidextrous arms on it, though, similar to something like a Radian or a Geissele handle but cheaper. It’s not as beefed up and you could always replace it with a Geissele or Radian.

The nice thing is that it’s out of the way and you don’t have to worry about hitting anything when you go to rack the handle. 


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Sig MPX Charging Handle

I will say if you have the collapsible brace and very large fingers, you might want to be careful about dropping your fingers too low because it could impact the brace’s mount.

This isn’t an issue for everybody and it’s definitely something you could train around by using the charging handle like rabbit ears.

In this case, the technique is going to dictate everything, but it is something to be aware of.


Sig MPX Handguard

The handguard on the SIG MPX is going to depend on the gun variant you get. I personally have the eight-inch barrel variant, which they no longer make.

The handguard on that version was quite long. I’ve since replaced it with a Lancer carbon fiber handguard, which is the same length and feels the same ergonomically but takes a little longer to heat up.

A buddy of mine has one of the Copperhead variants, and that handguard is very short and much harder to mount accessories to. That’s something we’ll cover below.


Sig MPX Trigger

The trigger on the MPX is essentially an AR-15 mil-spec trigger.

It’s mil-spec all the way.

To me, this feels just slightly lighter (maybe 15 percent lighter than my mil-spec AR-15s) but the reset and everything else feels exactly the same.

You have just the slightest bit of take-up/creep before you hit a wall and a rolling break. From there, you have a semi-authoritative reset right before the break again.

It’s a decent trigger, but if you’re a trigger stop you’ll definitely want to replace it.

SIG MPX Review Brace

Sig MPX Brace Collapsed

The SIG MPX has a Picatinny rail section at the rear of the gun that allows you to mount a variety of brace options.

SIG has its own set of braces — or you can mount an SB Tactical M1913-style brace — as well as the SIG MPX collapsing brace. 

Sig MPX Brace Half Position

There are two channels on the side of the receiver where collapsing brace rails will fit into so you can get an overall narrower profile of the gun.

I personally really liked this and like the collapsing brace much more than I thought I would.

It does make the gun wider and a little bit different, but it’s nice to have a gun that gets compact without a folding brace.

SIG MPX Accessories 

Sig MPX Bureau

Accessories do make or break a gun if you want something that looks sexy as hell.

The SIG MPX is a sexy-looking gun, but it looks a hell of a lot better accessorized properly. We’re going to cover everything that you can mount to this gun to truly make it into the gun of your dreams.

Maybe this is just a cool gun you want for the range or you’re building a fantastic, accurate movie-gun clone. No matter your speed, mounting the right accessories is very important.


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Optics Sig MPX Review

Sig MPX Left

This gun is very easy to mount optics to with a rail extending from the front to the rear of the receiver that accepts any Picatinny-mounted optics.

I personally have set the gun up with an EOTech.

The EOTech is a very wide optic and can have issues on some guns through the charging handle, but the AR-15-style charging handle presents no issues .


My gun didn’t come with iron sights, but you could easily mount AR-15 folding or flip-up sights on it. It’d have a decent sight radius, but you will want something that extends to the end of the handguard.

It’s going to depend on the variant you get; most of the guns that are shipping now have a four-and-a-half-inch barrel, so the sights will typically extend to the end of that barrel there. 

If you plan to mount a suppressor, you still might want to get an eight-inch handguard that will cover most of that suppressor and just make the gun look better.

If that’s the case, the gun might look a little bit funny with the front sight sitting four inches behind the front of the handguard.


Sig MPX Mod Button

Mounting a light to the SIG MPX is a little bit harder than you think.

There are Picatinny rail sections but things can get quite cramped, especially if you’re running the four and a half-inch barrel with a four-inch guard.

Running the gun with the eight-inch handguard really opens up your options.

Even with that being said, the handguard has a fairly large circumference. 

I’m running the gun with a Modlite attached to a ModButton that is then attached to a Picatinny rail insert that is on top of the Lancer handguard.

I can just fit my thumb on top of it ergonomically, but it’s not the easiest to use.

If I’m shooting the gun left-handed and want to activate the light, I have to use a tail switch on the rear of the light itself. That tail cap works well for me and my hand size but my grip is still somewhat compromised.

I can also use the ModButton, but that would put my arm into a very weird position.


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This gun would also work well if you were to mount something like a SureFire X300 at the 12 o’clock position on a Picatinny rail insert on the Lancer handguard.

Control Devices Sig MPX Review

You have three full Picatinny or M-LOK slots on the bottom of the Lancer handguard and the eight-inch variant makes it very easy to mount an angled foregrip.

Even if you have the four-inch version, you’re still going to have a slot and a half, so you’ll be able to mount almost any control device or angled foregrip to the gun that you desire.

I personally really like the C-shaped angled item that I have on the gun, but I’ve considered taking it off as sometimes I like just running the gun bare. I personally haven’t decided yet.


Mounting a sling on the MPX isn’t as easy as you would think.

There is a QD cup at the bottom of the rear of the receiver, so that does make things easier if you want them on a one-point sling.

I personally prefer two-point slings, and there isn’t a great place to mount a two-point on this gun. 


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You could definitely mount one on one of the four Picatinny rail sections of the receiver, or I can mount one to the M-LOK slots on the handguard.

I wish the Lancer handguard had M-LOK slots at the 11 o’clock position that I could more easily mount a sling too.

Unfortunately, all the positions on the handguard now would interfere with my grip, which isn’t great.

Shooting Experience

Sig MPX Lynx Defense Byte Right
Sig MPX fits perfect in the Lynx Defense Byte SMG Case

When you take this gun out of your Lynx defense bag at the range, you’re going to insert your first magazine, pull back the charging handle, let the bolt ride home, and then bring the gun up on target before flicking your safety off and pulling the trigger.

It’s just like an AR-15, but you have a lot less recoil and concussion.

If you’re shooting the gun suppressed, you’re going to be very surprised in a positive way.

This gun is extremely quiet thanks to the rotating-bolt system that keeps the action closed longer, making the gun much quieter than suppressed blowbacks.

I absolutely love shooting this gun suppressed and that’s what makes it one of my favorite firearms.

Don’t get me wrong: it’s fun to shoot unsuppressed, but shooting it suppressed just takes it to a whole other level. This is probably the best suppressed 9mm host out there. 

It’s a super ergonomic and fun gun to shoot. If you shoot a lot of 9mm and have access to heavier subsonic bullets, definitely check this firearm out.

If you have to shoot at indoor ranges that don’t allow rifle-caliber cartridges, then this is going to be a ton of fun for an AR-15 training replacement.

I just can’t say enough good things about how this gun shoots.

Final Conclusions Sig MPX Review

This gun has a lot of great options: it’s fun at the range, it could work for home defense, or it could even work as a truck gun. The options are really limitless. 

Sig MPX Left

The one major downside of this gun is going to be the price point.

This gun is priced at around $2,000, and that’s before you start adding accessories. I was lucky enough to pick up my gun used for a killer deal.

At $2,000, I probably would have never bought one of these. Now that I own one, however, I’d definitely consider buying one at around the standard price point.


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These guns are just fantastic, especially if you want to run it suppressed. if you don’t shoot a lot of 9mms and/or don’t shoot guns suppressed, it’s probably not worth it.

But if you shoot a lot on 9mm and use suppressors, you will not be disappointed with your purchase.

I hope you’ve enjoyed our Sig MPX Review.


  • Soft recoil impulse
  • Great suppressor host
  • Modularity
  • Tapered barrel (if you’re running a direct thread, can with their thread pitch)
  • Large aftermarket


  • Weight
  • Doesn’t have a 1/2×28 common thread pitch (only an issue for some)
  • Expensive
  • As large as an AR-15 In most formats

We’ve taken a look at a lot of Sig’s products you can see some of our Sig articles below:

7 Replies to “Sig MPX Review”

  1. Mark Romero says:

    The absolute WORST firearm I’ve ever owned! 8-9 lbs trigger, and would not reset until I pushed it forward with my finger. Every mag jammed with various ammo. STAY AWAY from this one!

    1. C christensen says:

      Put thousands of rounds through mine with zero issues. Bought a JP trigger springs kit and it’s held up and down to 4ish lbs.

    2. Chris says:

      Some MPX mags have a lot of spring tension and cause failures due to the bolt not having enough force to strip the next round out of the mag. Every new MPX mag I bought, I worked the spring a few times with a small wooden dowel or one of these wooden paint mixing sticks from Home Depot, then left the mag loaded for a week or two. I never had any failures after that. I’m not sure if this is still an issue with the newer MPX mags which are a made by a different manufacturer than before (it used to be Lancer, now it’s a diff. company).

    3. Springer Rider says:

      Had mine for two years. Have fired at least 2000 rounds of mixed ammo. I can’t remember a single failure. Maybe you had some Chinese knock off!!

    4. Larry Killen says:

      Did you take it to a gun Smith or contact Sig? I don’t think I’ve had a single jam or FTF and being up here on my own 18 acres, I’ve thrown out some rounds.

      I bet it you went to a good gun Smith, he’d straighten you out lickety split.

  2. Jose Reyes says:

    I have one i love this gun i shoot a 1000 rouns and cero issues for me is perfect.

  3. Larry Killen says:

    I love mine. I also have the matching air rifle. It saves on the ammo but still gives me target time.
    I can also shoot it in the basement and I have a 40 range set up down there.

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