The Maxim Defense SPS 505 PDX is a semi-automatic AR-pistol chambered in 5.56x45mm NATO with a 5.5-inch barrel, 20+1 round capacity, and an overall length of 18.75 inches. It weighs 5.10 lbs. The frame uses an aluminum lower with an Arid Brown polymer grip, and the pistol is optic-ready from the factory. 
 

Key Specifications 

• SKU: 2024020583 
• UPC: 680017508029 
• Condition: New in Box 
• Trigger Type: ALG Combat Trigger 
• Grip Material: Arid Brown Polymer 
• Stock Type: Synthetic 
• Weight: 5.10 lbs 
• Sights: Optic Ready 
• Overall Length: 18.75" 
• Barrel Length: 5.5" 
• Capacity: 20+1 Rounds 
• Action Type: Semi-Auto 
• Caliber: 5.56x45mm NATO 
   

Features 

 
The 5.5-inch barrel makes this one of the shorter AR-pistol configurations available in 5.56 NATO. At that length, the caliber gives up significant velocity compared to a 16-inch rifle, so understanding the ballistic trade-off matters for intended use. The HATEBRAKE muzzle device reduces muzzle rise and felt recoil, which helps with faster follow-up shots from a platform that otherwise would have more climb. 
 
The M-Lok handguard lets you attach lights, grips, or other accessories without proprietary adapters. The ALG Combat Trigger provides a smooth pull with a defined break, which is a step up from standard mil-spec triggers. The optic-ready design means no front sight tower blocking the rail.

The Maxim SPS 505 PDX draws a mix of enthusiasm and measured criticism, mostly from experienced AR-platform shooters.

Positive feedback centers on the compact form factor and the caliber choice. Owners who already run AR-15s appreciate sharing ammunition with a shorter platform. The build quality gets solid marks -- consistent performance with few malfunctions reported. Ergonomics are well-regarded, particularly the grip feel and overall balance for a sub-6-lb pistol.

The optic-ready setup is a consistent positive; buyers appreciate not having to remove factory hardware before mounting a red dot.

On the critical side, the 5.5-inch barrel's ballistic limitations in 5.56 NATO come up in more serious discussions -- some users question whether the caliber is well-suited to this barrel length for defensive applications. Trigger feel and reset draw some complaints from shooters accustomed to higher-end aftermarket triggers. Price is the most recurring objection, with some buyers feeling comparable platforms are available for less. Weight and bulk relative to dedicated pistols also come up for users who were expecting something more compact.