The RUK-9BT 4.5 inch 9mm pistol with arm brace from Rock River Arms is a compact AR-9 platform engineered for reliability, maneuverability, and modern pistol-caliber performance. Chambered in 9mm and built around a 4.5 inch chrome-lined barrel, this semi-automatic pistol utilizes a blowback operating system for consistent cycling and simplified maintenance. Its compact overall footprint makes it well suited for range use, training, and close-quarters applications while maintaining the familiar controls of an AR-style platform. Constructed with billet aluminum upper and lower receivers, the RUK-9BT features a Glock-compatible magazine system for broad magazine availability and cross-platform compatibility. A free-floating M-LOK handguard provides space for accessories, while flip-up sights offer immediate aiming capability. The pistol is equipped with a stabilizing arm brace for improved control and handling, along with a two-stage trigger for enhanced shooting consistency. Combining compact size, AR-15 ergonomics, and 9mm efficiency, this AR-9 pistol delivers a versatile and customizable platform for modern shooters.