The simple mesh of the Colt CM901.The Colt CM901 is a modular firearms platform that can be converted from an assault rifle to a designated marksman rifle as well as short barrel carbine without the use of tools.The CM901 (Colt Modular) weapons system is based on Colt's existing M16/M4 military designs. It shares the direct gas impingement operation, as well as much of the action, controls, and basic aesthetics with previous Colt rifle designs. The system's heart is a common lower receiver housing an enlarged magazine well that will accommodate larger caliber ammunition than NATO 5.5645mm rounds, ambidextrous controls for the bolt release mechanism, magazine release, and fire selector/safety lever, trigger group, pistol grip, telescopic stock, and buffer tube. The system will accept a series of upper receiver assemblies that contain the respective action required to accommodate the various caliber rounds accepted by the weapon. A re-designed upper receiver firing standard 5.56mm ammunition will be produced in various barrel lengths, all having a monolithic design with a full-length top rail, and three auxiliary rails for mounting accessories, free-floating barrels, and front and rear flip-up sights standard, when not using upgraded optics.
Upper receivers will be available in several calibers and barrel lengths, as short as 270 millimetres (10.7 in) for the 5.56mm model. The lower receiver will also accept older mil-spec M16 or M16 upper receivers with an adapter. Receivers will be available that accept 5.5645mm NATO NATO rounds, 6.843mm Remington SPC rounds, 7.6239mm rounds, and 7.6251mm NATO rounds. Each upper receiver has its own rail system, which allows scopes, or other optics to be pre-sighted for each configuration, and swapped quickly to perform different tasks.
The system can be anodized in a standard matte black finish, but has standard color options including Desert Brown, Digital Camouflage, and Vista Camouflage, which are applied during the anodizing process to prevent wear during use.