Maxim Defense PDX 505-SPS 5.56 NATO, 5.50 in, 20 + 1
Video review
Expert review
About this product
The Maxim Defense PDX 505-SPS is a Title II-manufactured AR pistol designed for short-range application, utilizing Maxim’s proprietary SCW Pistol System to eliminate the traditional buffer tube and collapse the rear profile. It is intended as an NFA-compliant, unstocked firearm from the factory chambered in 5.56 NATO, featuring a non-negotiable 5.50-inch barrel. The receiver configuration and weight distribution were developed specifically to counter the handling imbalance inherent to ultra-short-barreled rifle-caliber platforms.
What is the Maxim Defense PDX 505-SPS used for?
This platform is engineered for short-range deployment from vehicles, discrete transport, and as a primary weapon system for users subject to space constraints like private maritime security or rural homestead defense. Its 18.75-inch overall length fits inside a standard backpack or behind a truck seat, and the sling-ready QD mount permits rapid transition between supported positions during dynamic movement. You do not buy this for precision work past 100 yards; you buy it for its ability to deliver terminal ballistics in a package that measures under 19 inches.
How does the Maxim Defense PDX 505-SPS compare to building a 300 Blackout pistol?
The PDX 505-SPS is mechanically superior for maintaining consistent 5.56 NATO cycling in a 5.50-inch barrel compared to a DIY build using standard components. Where a home-built 5.56 pistol with a 7.5-inch barrel often requires an adjustable gas block, enhanced buffer spring, and specific ammunition to run reliably, Maxim’s integrated gas system and proprietary bolt carrier in the SCW system are optimized from the factory. A DIY build in 300 Blackout, like one based on a Stevens 334 action concept but for the AR platform, is ballistically better suppressed but locks you into a more expensive, niche cartridge.
What does it weigh and what are the dimensions?
The PDX 505-SPS weighs 5.10 pounds unloaded and measures 18.75 inches in overall length from the muzzle to the backplate of the SCW system. Its 5.50-inch cold hammer-forged barrel has a 1:7 twist rate, and the upper and lower receivers are machined from 7075-T6 aluminum with a Type III hardcoat anodized finish. When loaded with a standard 20-round PMAG, the weight increases to approximately 5.85 pounds—a balance point that sits directly over the grip, a critical detail for one-handed manipulation.
Who is this NOT for?
This pistol is not for the shooter seeking a low-cost introduction to the AR platform or for anyone primarily interested in long-range target shooting. The 5.56 NATO cartridge loses significant velocity and energy from a 5.50-inch barrel, producing massive muzzle flash and blast that is unpleasant and hearing-unsafe without a suppressor. If your primary use case is a general-purpose ranch rifle for 200-yard shots on predators, a traditional 16-inch AR-15 or even a bolt-action like the Stevens 334 in .243 Win is a more practical and ballistically efficient choice.
What's in the box?
The factory shipment includes the complete PDX 505-SPS upper and lower assembly, one 20-round Magpul PMAG, a Maxim Defense sling QD mount installed at the rear, and all required compliance paperwork documenting its status as a pistol. Notably absent is any form of optical sight, backup iron sights, or a sling—you are expected to supply those based on your intended application. The SCW buffer system is pre-assembled and requires no end-user adjustment, which is a deviation from kits that require headspacing or gas block alignment.
Is the Maxim Defense PDX 505-SPS worth it at $2245.50?
At $2245.50, this pistol commands a premium for its integrated engineering and NFA-compliant factory configuration, which saves you the $200 tax stamp, 8-12 month wait, and legal scrutiny of building your own Short-Barreled Rifle (SBR). You are paying for a turnkey system that has been reliability-tested with M855 ball ammunition, something a parts-kit build cannot guarantee without extensive tuning. For the user who requires a compact, duty-ready 5.56 platform and values regulatory simplicity over absolute lowest cost, the price is justified.
Specs at a glance
Pros & cons
What works
- 5.10 lb unloaded weight—nearly 1.5 lb lighter than a Daniel Defense DDM4 PDW with similar intent.
- 18.75-inch overall length fits in sub-20-inch interior compartments for discrete transport.
- SCW system eliminates snag-prone buffer tube, reducing rear profile by approximately 7 inches.
- Factory configured as a pistol, avoiding NFA Form 1 paperwork and $200 tax stamp for an SBR.
Trade-offs
- 5.56 NATO from a 5.50-inch barrel produces massive, uncontained muzzle blast—hearing protection is mandatory, and flash is significant even outdoors in daylight.
- Proprietary SCW bolt carrier and buffer system locks you into Maxim Defense for replacement parts, with lead times often exceeding 6 weeks.
- Requires specific high-pressure 5.56 NATO ammunition (M855-type) for reliable cycling; many commercial .223 Remington loads will cause short-stroking.
- No backup iron sights included—adds $150-$300 to initial cost for a quality set like Magpul MBUS Pro.
Key attributes
| upc | 680017508036 |
| manufacturer | Maxim Defense Industries |
| manufacturer part number | MXM50803 |
| action | Semi-Auto |
| barrel length | 5.50" |
| caliber/gauge | .223 REM/5.56 NATO |
| capacity | 20 + 1 |
| sights | Optic Ready |
Frequently asked questions
- Is it compatible with standard AR-15 parts?
- No, the upper receiver and the entire SCW Pistol System (bolt carrier group and proprietary buffer) are non-standard Maxim Defense components. You can use any Mil-Spec AR-15 lower parts kit, trigger, and pistol grip, but the rear assembly and bolt carrier are locked to Maxim's ecosystem. Attempting to install a standard AR-15 bolt carrier group will cause catastrophic failure, as the SCW system lacks a traditional buffer tube.
- Does it fit in a standard AR pistol case?
- Yes. With its 18.75-inch overall length, the PDX 505-SPS fits in any double-rifle case or specialized AR pistol case with interior dimensions exceeding 20 inches. For exact fit, we recommend a case like the Savior Equipment Specialist 30-inch double rifle bag, which provides 30 inches of internal length for the pistol, magazines, and a suppressor if configured.
- How long does shipping take to an FFL?
- Processing and shipment from Ironclad Armory typically takes 2-3 business days after order verification and FFL documentation is received. Transit time via common carriers like UPS or FedEx is an additional 2-5 business days depending on destination. You must coordinate directly with your chosen Federal Firearms Licensee (FFL) for receipt and background check initiation upon arrival.
- Can I return it if it doesn't cycle my ammunition?
- No. Firearms sales are final once transferred through an FFL due to federal regulations, unless the firearm has a demonstrable manufacturer defect. We test-fire each PDX with M855 5.56 NATO ball ammunition; if you experience failures with that specific ammo within the first 500 rounds, contact Maxim Defense directly for warranty service. Ammunition-related cycling issues with commercial .223 Remington are not grounds for return.
- Does this work with a SilencerCo Omega 36M suppressor?
- Yes, provided you use the correct muzzle device. The PDX 505-SPS ships with a standard A2 flash hider. You must purchase and install a compatible muzzle device, such as the SilencerCo ASR muzzle brake (part #AC2), and ensure your Omega 36M is configured with the ASR mounting module. Always verify centerfire rifle rating and minimum barrel length restrictions with your suppressor manufacturer—for the Omega 36M, the minimum for 5.56 NATO is 10 inches, so this 5.50-inch barrel is outside spec and voids the warranty.