The Bushmaster ACR (Adaptive Combat Rifle) is a modular, gas-piston-operated firearm designed for versatility and reliability in various tactical applications. Originally developed by Magpul as the Masada, the ACR was later refined and produced by Bushmaster, featuring a fully ambidextrous design with a monolithic aluminum upper receiver and a polymer lower for durability and weight reduction. It operates with a short-stroke gas piston system, which enhances reliability by reducing fouling compared to direct impingement systems. The rifle offers quick-change barrel capability, allowing users to switch between 8.25, 10.5, 14.5, 16.5, and 18.5" barrel lengths without specialized tools, making it adaptable for different roles. Chambered in 5.56 NATO with compatibility for caliber conversions, the ACR has a folding and fully adjustable stock for enhanced ergonomics. It includes an adjustable gas regulator for suppressed or unsuppressed operation, a full-length Picatinny rail for optics and accessories, and a proprietary handguard that supports modular attachments. The rifle's intuitive controls, including an ambidextrous bolt catch, magazine release, and fire selector, cater to both left- and right-handed users. While initially praised for its innovation, the ACR faced limited commercial success due to high costs and delayed caliber conversion kits. Despite this, it remains a highly adaptable platform valued by enthusiasts and professionals seeking a modern, mission-configurable rifle.