The Maxim Defense Industries SPS 505 PDX is a semi-automatic pistol chambered in 5.56x45mm NATO with a 5.5-inch barrel, 20+1 round capacity, and an anodized black finish. At 5.10 lbs it's heavier than most handguns but compact for what it's doing — running a rifle cartridge out of a pistol-length package. 
 

Key Specifications 

• Model: SPS 505 PDX 
• Caliber: 5.56x45mm NATO 
• Barrel Length: 5.5 inches 
• Capacity: 20+1 rounds (30-round magazine also compatible) 
• Weight: 5.10 lbs 
• Action: Semi-Auto 
• Sights: Optic Ready 
• Grip Material: Black Polymer 
• Stock Material: Synthetic 
• Finish Color: Anodized Black 
   

Detailed Features 

The M-LOK compatible handguard accepts lights, grips, and other accessories without adapters. The HATEBRAKE muzzle brake cuts recoil and muzzle rise noticeably, which matters when running 5.56 in a pistol-length platform. The ALG Combat Trigger has a smooth pull and a positive reset that experienced AR shooters will recognize. The SCW Buffer-Carrier System is Maxim's proprietary mechanism for cycling the action reliably at this barrel length while keeping the overall package short. 
 
The optic-ready top rail gives you a flat mount surface for red dots or low-power variables without needing a riser. 
 

Usage Scenarios 

At 5.5 inches of barrel, the PDX trades velocity for compactness — 5.56 is doing less ballistic work here than from a 16-inch carbine. That's an acceptable trade for home defense, where distances are short and maneuverability matters. Range use and competition shooting with this pistol classification are common applications as well.

Owners of the Maxim SPS 505 PDX in 5.56 NATO tend to focus on a consistent set of strengths and concerns.

The compact form factor gets the most positive attention. Running 5.56 NATO from a 5.5-inch barrel in a pistol configuration appeals to owners who want rifle-caliber capability without the length of a carbine. The HATEBRAKE muzzle device gets specific praise for actually managing recoil at this barrel length.

Construction quality is generally well-regarded. The Maxim-specific components — SCW buffer system, M-LOK handguard, ALG trigger — feel purpose-built rather than assembled from generic parts, which matters to buyers who've handled lower-end pistol builds.

AR-15 magazine compatibility comes up as a regular plus. Standard 20- and 30-round STANAG magazines work, which eliminates the proprietary-magazine problem that affects some compact firearms.

Price is the most debated aspect. The PDX is at the higher end of the 5.56 pistol market, and whether the Maxim-specific engineering justifies the premium over AR pistols built on standard components is a genuine point of disagreement among owners.

A few users mention accessory fit issues. The SPS 505's dimensions differ enough from a standard AR lower that some accessories don't drop in cleanly, which requires research before buying aftermarket parts.