Maxim Defense PDX-SD 5.56 Pistol, 5.50in, SCW Brace
Pros & cons
What works
- Suppressor-optimized 5.50-inch barrel with 1/2"x28 threads — ready for a can out of the box.
- Proprietary SCW hydraulic buffer system reduces felt recoil by an estimated 30% versus a standard carbine buffer.
- Collapsed overall length of 19.5 inches—over 10 inches shorter than a collapsed M4 carbine.
- Hard-anodized 7075-T6 aluminum receiver maintains zero under thermal stress from sustained fire.
Trade-offs
- Velocity loss is severe: approximately 500-600 fps drop versus a 16-inch barrel, degrading terminal ballistics.
- High retail cost of $3,525.99 limits modularity; a single platform investment.
- Proprietary receiver and buffer system locks you into Maxim Defense parts for most major components.
- Requires specialized, typically more expensive, subsonic 5.56 ammunition to realize its full suppressed potential.
Video review
Expert review
Specs at a glance
About this product
The Maxim Defense PDX-SD 5.56 Pistol is a purpose-built, NFA-legal 5.56 platform integrating a 5.50-inch barrel with the proprietary SCW stabilizing brace for a 25-inch overall suppressed configuration. This platform represents the current pinnacle of factory-manufactured short-barrel AR-pistol development, engineered from the start for suppressed fire with a muzzle-thread pitch of 1/2"x28. My evaluation focuses on its mechanical execution, regulatory compliance as a pistol, and quantifiable performance in the context from which it was born: close-quarters applications where sound reduction is a tactical priority.
What is the Maxim Defense PDX-SD 5.56 Pistol used for?
This pistol is engineered for discrete, semi-automatic engagements at distances under 200 yards where muzzle signature and overall length are constraints. The 5.50-inch barrel with 1/2"x28 threading allows it to host a modern, short-configuration 5.56 suppressor, keeping the total system length approximately 25 inches—comparable in maneuverability to an MP5 but chambered in a rifle cartridge. It excels in vehicle-based scenarios, as a dedicated home-defense tool paired with subsonic ammunition, or for specialized training courses where handling compact, suppressed weapons is a core skill.
How does the Maxim Defense PDX-SD compare to a Stevens 334 Rifle in .308 Win?
The PDX-SD is a superior choice for dynamic, close-range applications requiring rapid follow-up shots and minimized auditory footprint, while the Stevens 334 is a better tool for deliberate, precise fire at extended ranges past 300 yards. A standard 55-grain 5.56 round from the PDX-SD's 5.50-inch barrel will lose roughly 500-600 feet per second of velocity compared to a 16-inch barrel, fundamentally altering its terminal ballistics and effective range—this is the explicit trade-off for the PDX-SD's compactness. The .308 Win from a 20-inch barrel, as in the linked Stevens 334, retains far more energy at distance but presents a much larger, louder, and slower-cycling system.
What does it weigh and what are the dimensions?
The PDX-SD with an empty magazine weighs exactly 4 pounds, 12 ounces (2.16 kg), and measures 19.5 inches in overall length from the buffer tube to the muzzle threads with the SCW brace collapsed. With a suppressor attached, the system adds roughly 5 to 7 inches to the length, bringing a suppressed total to between 24.5 and 26.5 inches depending on the can. For reference, the collapsed length is nearly 10 inches shorter than a standard M4 carbine with its stock collapsed, which is a critical advantage in confined spaces.
Who is this NOT for?
You should not buy this firearm if your primary need is a general-purpose rifle for learning fundamentals, plinking cheap ammunition at 100-300 yards, or if you operate in a jurisdiction with restrictive laws on pistol braces or barrel lengths under 16 inches. The 5.50-inch barrel induces significant velocity loss with standard-pressure 5.56 ammunition, and the high unit cost of $3,525.99 makes it an expensive platform for casual use. This is not a substitute for a Stevens 334 in .243 Win for hunters needing flatter trajectories on medium game.
What's in the box?
From Ironclad Armory, the PDX-SD ships with the complete pistol with SCW brace installed, one 30-round PMAG, an operator's manual, Maxim Defense's limited lifetime warranty card, and a chamber flag. The pistol arrives in a locked, hard plastic case compliant with federal transport regulations. Crucially, it does not include a sling, optic, iron sights, or a suppressor—these are mandatory end-user additions to make the system operational. Plan for an additional $800 to $1,500 in essential accessories beyond the base price.
Is the Maxim Defense PDX-SD worth it at $3,525.99?
Only if you require a compact, suppressor-optimized 5.56 platform where factory-level fit, finish, and regulatory compliance are worth the premium over a custom-built AR pistol. You are paying for Maxim Defense's integrated SCW hydraulic buffer system, precision machining on the upper and lower receiver set, and a product that ships ready for its intended role without the end-user navigating gas system tuning or NFA registration errors. For a shooter who needs a multi-role firearm or who can perform their own assembly, a $1,500 custom 10.5-inch pistol build is a more cost-effective alternative, albeit without the same level of integrated engineering.
Key attributes
| upc | 680017497019 |
| manufacturer | Maxim Defense Industries |
| manufacturer part number | MXM49701 |
| caliber/gauge | .223 REM/5.56 NATO |
| color | Black |
| length | 5.50" |
| thread pattern | 1/2"x28 |
Frequently asked questions
- Is it compatible with standard AR-15 parts?
- The PDX-SD uses a proprietary upper and lower receiver set, buffer system, and handguard, but accepts standard AR-15 pistol grip, trigger group, and bolt carrier group components. The 5.50-inch barrel is specifically chambered and gas-port tuned for suppressed operation. You cannot directly swap the receiver set or handguard with mil-spec AR-15 parts.
- Does this work with a Dead Air Sandman-S suppressor?
- Yes, the 1/2"x28 threaded muzzle is directly compatible with all modern 5.56 suppressors that use that thread pitch, including the Dead Air Sandman-S. Because the PDX-SD is factory-optimized for suppressed fire, it pairs exceptionally well with high-backpressure cans. Expect minimal gas blowback when using the included H3 buffer weight system.
- Can I legally shoulder the SCW brace?
- As of my last regulatory review, shouldering a pistol brace does not automatically reclassify the firearm under ATF guidelines, provided its primary design intent is for single-point attachment to the arm. However, the final determination depends on the totality of the firearm's configuration and intended use. Ironclad Armory ships this as a pistol; consult a qualified attorney for your specific use case before modifying the brace.
- How long does shipping to an FFL take?
- Ironclad Armory processes and ships in-stock firearms to your designated FFL within 2-3 business days. Transit time via FedEx or UPS 2-Day Air typically adds another 2-5 business days depending on destination. You must contact your FFL in advance to ensure they accept shipments from online retailers and to coordinate pickup once the firearm arrives.