We’ve been hearing a lot about SIG SAUER’s new pistol caliber personal defense weapon, the MPX, ever since it was unveiled at SHOT Show a few years back. At the time the plan was to release both a pistol version of the firearm (with short barrel and no stock) as well as one with a permanently attached muzzle brake that would bring the barrel length to an ATF-appeasing 16″ in length. While the fate of that brake-festooned version is still in legal limbo, SIG is planning on finally releasing the pistol version to the civilian markets soon. We had an opportunity to get our hands on the gun and get some trigger time before anyone else, and boy is this thing a blast . . .
The gun was designed from the ground up to be a replacement for the aging MP5 submachine gun currently in arsenals world-wide. While the MP5 was a brilliant design when it came out in 1966, the state of the firearms design art has changed pretty dramatically since then and the gun now seems dated by comparison. For example, stamped sheet metal and riveted trunions are no longer staples of firearms design these days. H&K tried to update their iconic firearm by releasing the UMP, but its plastic-based design suffered from reliability and accuracy issues and hasn’t seen the widespread adoption its predecessor did.
The MPX solves these issues by using the overall design of the AR-15 platform and modifying the dimensions to better suit pistol caliber ammunition. This allows for a firearm that the end user in the field can modify it on the fly for whatever mission they are facing, makes maintenance of the firearms much easier, and cuts down on the overall size of the gun.
Here’s another issue inherent with the roller-delayed blowback system of the MP5 — you need to change almost everything in the bolt carrier when you swap between projectile weights. Moving from 115 grain frangible rounds to 147 grain hollow points? Break out the armorer’s kit. With the MPX, the gun just works no matter what you feed it. No changes required.
SIG SAUER not only improved the operating mechanism of the gun, but also worked with Lancer to come up with a new polymer magazine design. Using the same tricks that Lancer uses in their AR-15 mags, they produced a lightweight, translucent magazine that has a steel insert that strengthens the feed lips and the catch slot as well, adding a ton of durability to the design. Oh, and they look bad-ass too.
Another benefit to the new mags is that the gun’s cyclic firing rate can be jacked way up thanks to their design. The version we played with was set to about 1,200 rounds per minute, which is well above the ~700 rpm rate of an MP5. The reason the gun is set so high is that the gun can feed reliably even at extremely high cyclic rates. The magazines are designed to present the next round almost directly in line with the chamber, something that the MP5 doesn’t do. So while an MP5 will start having serious reliability issues when running at anything over 1,000 RPM, the MPX has been reliably tested at well over 2,000 RPM.
While the old MP5 design did come with a few options in terms of stock attachments, swapping one for another was a bit of a production, not something you could do quickly and on the fly. Thanks to the fact that the operating system of the MPX and MCX rifles are completely contained within the upper receiver, there’s no longer a need for a buffer tube or receiver extension. So SIG has decided to swap the old receiver extension for a Picatinny rail, and they’re making a boatload of different stocks that will attach to the rifle at that point. Everything from a side-folding stock to the nifty Honey Badger-esque sliding wire frame stock will attach to this short rail section. And because it’s a standard design, anyone can make alternate stocks for it as well.
Everything about this gun can be changed, from the stock to the handguards to the muzzle device. The current version of the gun sports a typical Picatinny rail system, but the R&D guys say they’ll probably be switching to the increasingly popular keymod system soon.
Out on the range, the MPX shoots like an absolute dream. Recoil is soft and straight, meaning that the gun is very easy to control even when you crank it over to the “auto” setting. The wire frame stock is actually pretty comfortable and the trigger is crisp and clean. The controls felt very familiar, just like the AR-15 we’ve all come to know and love.
The version we played with was the standard LE/MIL version, which SIG typically shows off with the removable two-chamber silencer. The small can might not seem very potent compared to the massive suppressors we’re used to seeing, but it’s so efficient that those two small chambers of suppression are all that’s needed to make the firearm hearing-safe at the shooter’s ear. It’s not exactly silent, but it’s damn near pleasant.
Thanks to our friends at the ATF, SIG will be shipping a pistol version of this gun (with SIG Sauer’s famous pistol arm brace as an option) to the civilian market and holding off on a rifle length version. Apparently the gun is designed to only use a short barrel, so making a proper 16″ barrel for the gun would take a bit of re-working in the operating bits of the firearm. But the pistol version will indeed be shipping shortly to the US commercial market. And when it does we’ll have a full review.