The Sig MPX caught everyone’s attention from the very beginning. After having shot one a few weeks ago I can understand why. Man is this sub gun fun to shoot! Probably the best news I can pass along is the civilian pistol model in semi-auto will be available to civilians pretty soon.

The entire idea behind the MPX was to improve on and replace the H&K MP5 and so the MP5-SD is aimed at the military and police market. Now in my mind replacing the MP5 is a tall order. I’ve enjoyed the MP5 for many years and so I wasn’t by any means convinced Sig could come up with something as good. I had an issue MP5-SD for a number of years and it is the gold standard by which all others are measured.

The only downside I saw with the MP5 was that it came in only 9mm (well, there were some high caliber version produced for a while, such as the FBI’s legendary MP5/10 in 10mm Auto, but they were discontinued). The user on the other hand can change the MPX caliber in the field. You can take your MPX and change it to 9MM, 40 S&W or 357 Sig. in a matter of minutes. You can also carry extra barrels of various lengths and change those out easily.

When designing the MPX Sig based it roughly on the M16 but with considerable internal changes. The MPX is also the first sub gun to fire from a closed and locked bolt which looks very much like an M16 bolt. MPX’s are also designed around a short stroke piston system.

STATS FOR MPX SD

Item Number MPX-SD
Caliber 9mm NATO, Converts to .357SIG or .40S&W
Action Type Select Fire (LE/GOVT ONLY)
Operating System Closed, fully locked short stroke pushrod gas system
Overall Length (Telescoping Stock) Min (Closed) 688 mm/28.1 in, Max (Open) 808 mm/31.8 in
Overall Length (Folding Stock) Min (Closed) 653 mm/25.7 in, Max (Open) 838 mm/33.0 in
Overall Width 52 mm/2.0 in
Barrel Length 165 mm/6.5 in
Sight Radius 371 mm/14.6 in
Cyclic Rate 850 RPM
Features Easily converts to 9 mm NATO, .357SIG, or .40S&W, User-configurable stock system: telescoping, folding, intergrally suppressed
MSRP Not Available

There are two types of suppressors for the MPX. One is a threaded short one while the other is integral and wears the name MPX-SD. The SD wears a 6.5 inch barrel. Several butt stocks are available all of which telescope to three positions. Using a small Picatinny rail that is attached to the rear of the receiver easily allows them to be changed.

Going back to the effort to best the H&K MP5-SD. The decibel level on the H&K is measured at right at 135 decibels. The MPX-SD with integral suppressor comes in at 128 decibels. This might not sound like much but it is a considerable difference. This would make the MPX the quietist sub gun in the world, which was the goal. The integral suppressor used at the Sig Academy was so new it was still in the white and not even coated yet.

Magazines for all MPX’s are translucent and made especially for the MPX by Lancer. The magazine is critical to the MPX when it comes time to adjust the rate of fire. The standard factory rate is 850 rpms but can be pushed up to 1200 rpms. The MPX has been tested as high as 2000 rpms.

Shooting the MPX-SD is a pure joy. The rate of fire allows the user to fire three round burst simply by trigger control. After a few runs I was able to fire single rounds with it set to full auto. Leaving it on full auto and dumping a full magazine is easy. Easy in that it’s easy to keep on target. The gun just doesn’t walk around it just sits there banging the target with 9MM ball as well as using the new Sig 9MM HP loads. When shooting subsonic rounds it was ridiculously quiet.

The first photo shows me firing the last mag of the day. You can see from the photo there is no muzzle rise. Two empty cases are in the air if you look closely. Also, my thanks to Sig Forum for use of the photo.

I’ve listed photos of all of the variants. The pistol is the one that will be sold to the public. In conclusion I think Sig, over time, will have achieved their goal of replacing the H&K MP5 SD. This Sig is all you could ask for in a sub gun.

MPX 8 inch barrel

MPX-K 4.5 inch barrel

MPX-P

MPX-SD

MPX P SB