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Maxim Defense PDX SD: Short, Silent, & Soft Shooting [Review]

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Photos by Tamara Keel with Dave Merrill

Back in 2019, Maxim Defense won RECOIL’s Best of SHOT award and also graced the cover of RECOIL Issue 41 when they released the PDX, a short 5.5-inch barreled PDW with an overall length of 18.75 inches and offered in 5.56mm, .300BLK, and — our favorite in this form — 7.62x39mm. Systems this small have been attempted before, but, importantly, the Maxim Defense PDX actually worked. They cracked the code. 

When it comes to a gun that’s stubby and stashable while also chambered in a rifle caliber, the clandestine capability also comes with an awful lot of bang. Maxim Defense spent the following years developing a fix for this next part of the problem — making it more stealthy with all the blast and gas. 

With lessons learned from the development of their MSX-240 suppressor that withstands the rigors of a full-auto 7.62x51mm belt-fed, along with further design insights stemming from their DSX silencer line, last year at CANCON 2022 Maxim Defense finally showed off their latest: the PDX SD.

At a mere 23.75 inches tail-to-tip, the PDX SD is only 5 inches longer than a traditional unsuppressed Maxim Defense PDX, yet still sits below the length threshold of any rifle you can buy off-the-shelf at Cabela’s. It’s seriously small, and the next thing you’ll notice is exactly how fat the silencer section is. Jokingly dubbed “the soup can,” the silencer that sits on the SD has an outer diameter of 2.25 inches.

Some Maxim Defense soup can prototypes, with the PDX silencer on the far left.


We’ve reported in the past that the U.S. Military is taking steps toward an all-suppressed army, and they’re starting with SOCOM. While other companies are working on retrofits (and Maxim is doing some of that themselves), Maxim took a different approach here.  

President and CEO of Maxim Defense, Michael Windfeldt, says, “The standard way of doing business is picking the rifle, then adding the suppressor — adding to the gas pressure problem. So, then they [DoD] ask for a lower-flow suppressor. 

We take the systematic approach; we’re designing our weapons to always be suppressed. The suppressor is the muzzle device to those systems, and designed and tuned for the rifle. The PDX SD is a special-purpose rifle, required to be very small and hearing safe.”


One major difference between the PDX SD and what we’d normally call an “integral” is that the silencer unit itself can be removed. What makes us still classify the Maxim Defense PDX SD as an integral is that the silencer was specifically designed for the gun, and the gun specifically for the silencer — they’re a system and need to work together in order to work at all. 

Designing the suppressor module to be removable not only makes basic maintenance like cleaning more traditional than with other integrals, importantly it means that parts can be easily and readily upgraded and replaced with newer technology down the line.  

Just 23.75 inches long.

This is much harder than it looks, especially when everything from the barrel to the bolt carrier to the buttstock add additional variables to contend with. 

Since the launch of the PDX back in 2019 and the setup you see here now, we’ve shot multiple protype iterations of the PDX SD. We started with Mk1, then Mk2, and Mk-god-only-knows before you see what’s here today.

Maxim’s director of engineering, Patrick Tramble, ran off a laundry list of both major and minor challenges they had to overcome to produce the PDX SD. 

Needless to say, the PDX SD has even more custom work than the original PDX, with the heaviest lifting taking place in the balance of size, sound, and reliability. With its own custom-length gas system, handguard, and proprietary sealing mechanism, you won’t be doing much parts-swapping or building a PDX SD 1:1 in your garage, at least not if you want it to work. 

The PDX SD was designed as a straight-out-of-the-box solution. As a special-purpose system, if it doesn’t make sense to you, then it wasn’t made for you. 


We should’ve known the PDX SD would be special when the folks at Maxim broke out their cellphone cameras as we picked it up at the range. They’ve done this to us before with premiere products to catch our unedited reactions, first with the original PDX and later with their have-a-convo-while-shooting M240 silencer. But having experienced previous PDX SD prototypes, the thought didn’t even cross the mind. 

The very first shot felt too light, like a misfire of a rifle that didn’t properly cycle. That worry was dashed with another pull of the trigger, followed by the splash of steel downrange. The PDX SD is so properly balanced and the gas so finely tuned it shoots like a high-end competition gun with a bi-gassed brake on the end, except it’s shorter than two soda bottles and is hearing safe. Seriously? Seriously. 

Maxim Defense PDX SD

  • Barrel Length: 5.5 inches
  • Overall length: 23.75 inches
  • Weight: 7.5 pounds


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