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Sig MPX Optimized: MPXSD Integrally Suppressed

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It’s no secret that pistol-caliber carbines are an excellent choice for home defense or as “truck guns.” In that class, there are a couple of great options available — with the SIG MPX being a Cadillac offering. The original 8-inch-barreled version was intended to fill the same-size envelope as the much-vaunted HK MP5 with a modern gas system, AR-style controls, and modularity at both ends with M-LOK handguard and Picatinny rail endcap. With all this in mind, we wanted to dedicate an Optimized column to setting up our version of the ideal home-defense-oriented MPX carbine. We started with a legacy 8-inch model, which we Form 1’d to run as an SBR, but several shorter variations are now available. We were able to clip a little bit of overall length by swapping the telescoping stock for SIG’s minimalist side folder. This short, rigid stock folds quickly but deploys with solid lockup, making it ideal for PDW applications like this.

One of the first things we wanted to address was sound suppression. This isn’t an option in some parts of the country but barring local restrictions, if you’re able to suppress your home-defense gun we strongly suggest you consider it. Traditional direct-thread cans are plentiful in 9mm with options all up and down the size and cost scale; we went a step further and contacted a small company called D3LLC in Arizona that offers a specialized, integrally suppressed version of the SIG MPX. 

Their system requires customers send in their MPX upper to have a series of ports drilled into the barrel itself, much like the original MP5SDs. In fact, their “full-size” integral upper, paired with SIG’s own telescoping MPX stock, gives you a platform the exact same length of an original MP5SD — which was the preeminent choice for quiet CQB by special military and police teams for decades. For a touch of personal flare, the entire gun was finished with Cerakote by Ronin Arms, also based in Arizona. They work closely with D3 so if you’d like your newly suppressed gun refinished while they have it, they can coordinate in tandem.

There are a few idiosyncrasies to be aware of with the D3 setup. First off, it won’t cycle subsonic ammunition. Like the MP5SD, the D3 MPX SD works by reducing the velocity of standard ammunition to subsonic levels through barrel porting, meaning you can plug in whatever defensive ammo you prefer and still get the highest possible level of noise reduction. Another note is that you cannot use the factory handguard, but the Midwest Industries M-LOK handguard works perfectly and offers additional M-LOK slots for accessory mounting. However, even with the larger MI unit, there’s minimal clearance between the can and the inside edges of the handguard. We were still able to mount all our desired accessories, but it did require grinding down some of the screws on our M-LOK mounts to avoid screwing into the body of the can itself (we’ve run into the same issue with other integrals).


The D3LLC integral suppressor uses a series of barrel ports to get whisper-quiet results even out of standard velocity ammunition.

Speaking of accessories, we wanted to keep our SIG MPX SD as lean as possible, focusing on its specific role as a hearing-safe home-defense gun. As such, a dependable white light is essential. We went with the Cloud Defensive REIN. The REIN
is a dedicated weapon light that offers a whopping 1,400 lumens and 60,000 candela. Runtime is approximately two hours off a fully charged 18650 battery. 

Control-wise, the REIN has both a two-button tape switch (dedicated buttons for momentary and constant-on) and a “clicky” rear tail cap. The two activation methods work independent of each other so that, even if the wire on your tape switch is damaged or severed, the tail cap will still run the light.

Since the REIN body is compatible with current standard mounts, we attached an Arisaka Defense in-line mount to keep the light forward-mounted and tight against the suppressor.  

We also wanted a small red-dot optic with a wide-open objective to maximize engagement speed when faced with the potential of an across-the-coffee-table gunfight. The Trijicon MRO fills this niche nicely, with its small 2 MOA dot and flared front window. The Scalarworks LEAP mount adds almost no weight while securing firmly with a thumb-dial tension screw and a mild forward bias.

Finally, for a little bit of extra control when driving the gun, we changed the stock pistol grip for a heavily textured G10 model from VZ Grips, as well as adding their M-LOK cover panels and finger stop. The deep texturing in VZ’s products gives you a rock-solid grip as soon as you close your hands on the weapon, and the finger-stop panel set doesn’t add the bulk or chopped broom handle protrusion of a forward vertical grip. It also positions your support hand perfectly to hit that 12-o’clock-mounted tape switch.

This setup gives you a suppressed, red dot’d, white light-equipped bedside gun with 30 rounds on tap and two extra points of contact over a nightstand pistol. It does an excellent job of filling the role of a “semi-auto subgun” for home defense. Some of the unique requirements of the D3 MPX SD package definitely place it into the “specialist” category compared to just mounting a can to the end of the barrel, but the result is a compact weapon that’s “Hollywood quiet” even with standard defensive ammo. However, if you’re looking for a dedicated defensive PCC and don’t mind a two-stamp solution, the MPX SD provides everything you could ask for in a package small enough to stay in your closet, cubby, or behind the bedroom door. 


Sig Sauer:
Ronin Arms:
VZ Grips:
Cloud Defensive:

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  • Nick says:

    Not cycling subsonic ammo seems like a major downside. The decrease in sound signature from subsonic 9mm rounds is fantastic. Perhaps it can be tuned to run it. My regular old MPX’s with cans of various types cycle it fine.

  • Nick says:

    I see, re-read that part – it reduces supersonic to subsonic by means of its operation. A good test is in order!

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  • Not cycling subsonic ammo seems like a major downside. The decrease in sound signature from subsonic 9mm rounds is fantastic. Perhaps it can be tuned to run it. My regular old MPX's with cans of various types cycle it fine.

  • I see, re-read that part - it reduces supersonic to subsonic by means of its operation. A good test is in order!

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