SIG Sauer seems poised to take over the world these days. It seems like they have a winner in every market segment except kitchen sinks, and they are probably working on kitchen sinks right now. A huge win for SIG has been the MPX family of pistol caliber carbines (PCC), and this week we got our hands on one to test.
- Cartridge: 9mm
- Barrel: 8 in.; 1:10-in. twist
- Overall Length: 16.7 in. (stock folded); 24 in. (stock extended)
- Weight: 6.1 lbs.
- Trigger: 5 lbs., 8 0z. – 9 lbs.
- Sights: N/A
- Finish: Matte Black
- Capacity: 30+1 rds.
- MSRP: $2,084
- Manufacturer: SIG Sauer
Our version of the MPX was actually the MPX PSB (pistol stabiliizng brace) pistol version, which I guess makes it the pistol caliber pistol? The not an SBR but totally a semiautomatic 9mm sub gun? What the MPX represents is a leap forward in real sub-machine guns, with many flavors of semiauto, civilian-legal variations. The controls are all AR-15 in style, but this isn’t just another AR scaled to fit pistol bullets. The MPX was designed from the ground up as a new platform, with a retention of the design characteristics from an AR that it made sense to steal. This cuts the learning curve to zero, and also fits the MPX nicely into applications where a rifle is too much, but a pistol is too little.
The pistol version ships with the ubiquitous SIG “Arm Brace”, with a slightly extended length from other versions I have seen. It is about 3 inches longer that the AR versions, classic SIG sticking it to the man every chance they get. Because the MPX doesn’t require a buffer, this brace isn’t also a buffer tube. More on that in a minute. The brace is attached to a folding hinge, which mounts on the MPX via a Picatinny rail on the back of the receiver. The folding hinge bolts to the Picatinny for a rock-solid joint. When you shoot the MPX with, uh, the arm brace velcroed in place, there is no movement in the stock, which is awesome. The hinge is a little tight, it takes some force to unlock, but it works great.
Article Continued Below:
The receiver set looks very similar to an AR, and it is fully ambidextrous including the charging handle. Your welcome, wrong handers. The magazine release button has gotten a little redesign, it is about twice the size of a normal AR-15 on the right side, and the paddle on the left is about the size of a regulation normal one. The safety selector is AR similar on the left, and little shorter that your old familiar controls on the right. The left side bolt release has an added bit of length to the bottom, making it ¾ inches wide, very easy to press for locking the bolt back. The right side bolt release is absolutely massive, and you can easily reach it with your trigger finger. Only the left side will lock the bolt to the rear, but both sides release it with ease. The magazine well is slightly flared, which really helps facilitate quick reloads. The MPX runs on a proprietary Sig magazine, which gave me zero problems. The magazine is clear plastic with steel feed lips, and runs buttery smooth. Loading the magazine is easy, no Uzi magazine problems for this little guy. We only had one magazine for testing, the factory standard 30 rounder. I was very happy with how easy the magazine came apart for the installation of my Taran Tactical Innovations +10 extension. TTI had just shipped the new aluminum extension in Coyote Bronze, and it ran like a champ. This extension does not require a new spring, which also tells me SIG was serious on spring tension. Adding 10 rounds is no small feat, so the factory 30 round was absolutely meant to work in all conditions, for a very long time.
The upper and lower come apart with just like an AR, with a takedown pin front and rear of the receiver. This is where the similarities end though. The MPX doesn’t use a scaled-down AR bolt, though both are cam based locking with rotating lugs. The MPX has two springs on top of the bolt that recoil against the receiver, and push the bolt back into the chamber. This cuts down on the overall size of the bolt, and also means the MPX works normally with the stock folded or taken off in the pistol variant. No nubby buffer tube required. At the back of the receiver is a large polymer ring, which absorbs the impact of the bolt, and keeps your steel bolt from smacking the aluminum receiver.
How It Works
The action is neither direct impingement or blowback, it is a short stroke piston system. This keeps most of the filth from pistol rounds out of the receiver and has proved to be very reliable. The barrel on the pistol version is 8 inches, but has the new MPX quick barrel change system just like the carbine. If you push out the front takedown pin, the handguard pulls straight off. This exposes two hex screws, pull those out, and the barrel comes right off. This makes barrel changes a snap, and in the future caliber conversions will be easy as the day is long. One of my only complaints, SIG put a 13.5×1 metric thread pitch on the barrel. If you use direct thread suppressors, better make sure you can get an adaptor.
The MPX doesn’t ship with iron sights, but this is a pretty easy fix. We are talking about SIG after all. For testing, we were also provided a Romeo5 1x20mm compact red dot sight. This optic features a 2 MOA red dot with 10 illumination settings, 8 for daylight and 2 for night vision. This sight also features MOTAC, motion activated illumination system, which powers up when it senses motion, and powers down when it doesn’t. The dot is very bright; I had no trouble finding a setting for broad daylight. The controls are a bit different, but it worked just like an Aimpoint. In the box are mounts for both low and 1.41 inch co-witness bases, which is a nice touch. I liked the high mount for the MPX pistol, and will try the low mount next week on a rifle 45-degree offset.
A Little Extra
In keeping with the SIG complete package, what could possibly make this any better? How about a training tool to go with it? Also available from SIG, we received an MPX airgun and target system. SIG has really come out swinging on this front; they have introduced several airgun systems over the last year. The MPX air comes with a real buttstock since it isn’t a firearm, but is otherwise identical to the MPX pistol. The airgun runs off of CO2 cartridges and fires .177 caliber steel pellets. This is no child’s toy, as the pellets reach up to 600 feet per second (fps). It even comes with an incredibly similar red dot sight. Big applause to SIG Sauer on this one, replica airsoft or pellet guns are a fantastic training tool to round out a system. The savings in ammunition cost are staggering, and it isn’t hard to set up an airsoft range in your garage. Can’t say the same for 9mm, that is a certainty.
This is the first time I have ever had optics, gun, and ammo all made by the same manufacturer, which is pretty wild to consider. If I had a better license, I could have gone ahead with a suppressor as well. A training replica gun is pretty awesome as well, and pellets are arguably a better option than a .22 LR conversion. Have you tried to buy .22 recently? The MPX ran like a sewing machine and had zero malfunctions. Magazines aren’t cheap, but they are available, and it’s nice to have aftermarket support already from places like Taran Tactical Innovations. A 40 round sub gun magazine is pretty hard to argue with. There was a lot of winning with this system. The SIG 115 grain ran like a champ.
So what was the bad? I only have a couple of complaints. One is the trigger, which is less than good. To be fair, it is about like a Mil-Spec AR. The big problem is a replacement. I don’t believe in bad triggers, especially after I pay $2,000 for a gun. AR-15 triggers fit the MPX, but SIG says the new gun is very hard on fire control systems.
Secondly, I would have much rather had this gun for testing in the carbine variant. I understand why SIG makes a pistol version, some people are really in love with this and don’t want to SBR. But for a shake out of a weapon, it is a lot easier with a real stock and a grown up barrel. A 16-inch carbine version is on the market right now, and that is a much better choice for most consumers. Even in the pistol version though, I would have preferred to see an 11-inch barrel. This has nothing to do with velocity, and everything to do with the hand stop. On the 8-inch barrel, even with the hand stop installed, it is entirely too easy to get a finger near the muzzlebrake. I have seen this happen with an MP5, and the result isn’t pretty. If you buy the pistol version, be extremely careful.
For more information, visit https://www.sigsauer.com/store/sig-mpx-psb.html .
To purchase an MPX on GunsAmerica.com, click this link: https://www.gunsamerica.com/Search.aspx?Keyword=MPX.