Maxim Sps Pdx Upper 762x39 5.5"

The Maxim SPS PDX Upper 762x39 5.5" is a purpose-built upper receiver assembly engineered for shooters who demand modularity, reliability, and compact performance in an intermediate cartridge platform. Designed by Maxim Defense Industries—a manufacturer known for innovation in short-barrel rifle systems—this upper serves law enforcement, military personnel, and civilian operators seeking a drop-in solution for 7.62×39 NATO ammunition in a truly compact profile.

The 5.5-inch barrel length positions this upper at the intersection of portability and ballistic efficiency, ideal for close-quarters environments where standard rifle length compromises maneuverability. This upper receiver assembly integrates Maxim's SPS (Short Piston System) platform, which leverages a piston-driven operating system to enhance reliability and reduce carrier tilt—critical factors in short-barrel configurations where gas tube dwell times are compressed. The 5.5-inch barrel maintains adequate velocity for 7.62×39 rounds while keeping overall length under 26 inches when mated to a standard lower receiver, supporting both suppressed and unsuppressed operation.

Construction emphasizes 4150 chrome-moly steel and hard-coat anodized aluminum throughout, ensuring durability under sustained fire and field deployment. The PDX designation indicates optimization for duty-class performance, with proper ejection, smooth feeding, and minimal maintenance requirements even in adverse conditions. This upper assembly is compatible with Mil-Spec AR-15 lower receivers, making it a versatile choice for various applications.