600 meters from an M4 carbine – USSOCOM's ambitious plan

The United States Special Operations Command (USSOCOM) has launched the Hypervelocity Improved Capability Assault Rifle (HICAR) program, aimed at developing a new carbine capable of effectively engaging targets at ranges exceeding 600 meters. Currently used by special forces, the M4A1 carbines equipped with the URG-I setup achieve a practical effective range of around 300 meters, which can be insufficient on the modern battlefield.

A key element of the program is the new 5.56×45 mm M855A1+ ammunition with a very high muzzle velocity. Chamber pressure is expected to reach approximately 82,000 psi (around 565 megapascals), representing a significant increase compared to standard military ammunition.

The new weapon must maintain full compatibility with both the M855A1 and Mk262 ammunition already in military stockpiles, as well as the new M855A1+ round. This requires the development of a design capable of withstanding significantly higher stresses than current M4-family carbines.

The technical requirements are very specific. The barrel must be 11–12 inches long. The weapon’s weight, without a magazine and suppressor, must not exceed 3.63 kilograms (8 pounds), with a desired target of around 2.95 kilograms (6.5 pounds). The design must work with currently used M4A1 lower receivers without modification and remain compatible with accessories used by USSOCOM. The HUXWRX Flow 556k suppressor will be used during testing.

The new design is expected to deliver accuracy of around 1 MOA without a suppressor, and ultimately even 0.5 MOA. The required reliability is at least 800 rounds between stoppages on average, with a target of 1,600 rounds. The minimum barrel life is specified at 8,000 rounds when using M855A1+ ammunition, although SOCOM would prefer to see results closer to 20,000 rounds.

The requirements list also includes fully ambidextrous controls, an M-LOK mounting system, a single-point sling attachment, resistance to submersion in water at a depth of approximately 90 centimeters for two hours, and operation in temperatures ranging from about -40°C to +74°C.

The biggest unknown remains whether ammunition generating such high pressures can be used over extended periods. If manufacturers manage to develop a sufficiently durable design, HICAR could become one of the most significant upgrades to the M4 platform in many years.

The program also raises questions about the future of the U.S. Next Generation Squad Weapon (NGSW) program, which uses 6.8 mm ammunition. If the new 5.56 mm round can achieve an effective range exceeding 600 meters while maintaining lower weight, higher magazine capacity, and lower costs, some of the arguments in favor of the new caliber may lose relevance. On the other hand, 6.8 mm ammunition still offers greater projectile energy and improved penetration against modern ballistic protection.

The first technical concepts are expected to be presented in June 2026, with project demonstrations scheduled for September. However, the biggest question remains whether a design capable of long-term operation under the pressures generated by the new ammunition already exists, or if manufacturers are only just beginning work on it.

Source: The Firearm Blog, SOCOM