USSOCOM upgrades M4A1 carbines
US Special Operations Forces soldiers with M4A1 carbines.
The U.S. Special Operations Command plans to modernize its existing M4A1 assault rifles. By replacing key components and introducing a new cartridge, it aims to improve the rifle's primary firepower. weaponsThe project, designated HICAR, is currently seeking potential contractors. The first results are expected in early fall.
The problem of characteristics
The M4A1 carbine, when chambered for the standard 5,56×45mm M855 cartridge, has an effective range of 600 meters. However, in real combat, a number of factors reduce this range. For example, when the enemy is wearing personal protective equipment, the effective range drops by half or more—to approximately 300 meters or less.
The US Army is addressing this issue radically through the NGSW program, which is adopting a new rifle system (the XM7 rifle) chambered for the more powerful 6,8×51mm cartridge. US Special Operations Command (USSOCOM) has chosen a different approach: it has decided to avoid a full-scale rearmament and caliber change, maintaining a unified supply chain for 5,56mm ammunition.
The command is launching the HICAR (Hypervelocity Enhanced Capability Assault Rifle) program. The very name, with its reference to "hypervelocity," is a marketing ploy: it doesn't refer to hypersonic speeds in the physical sense, but rather to an increase in muzzle velocity. The program's goal is to upgrade the existing M4A1 carbine with the improved 5,56×45mm cartridge. These measures are expected to deliver the desired performance gains at a limited cost.
On May 18, 2026, USSOCOM posted the first "request for information" on the HICAR project on the government contracting portal. The command is accepting applications from companies interested in participating in the program until June 8. By the end of the month, the list of participants will be determined, and contracts for project development will be awarded shortly thereafter.
The first results of the work are expected in just four months. In mid-September, the first demonstration and comparative tests of the upgraded carbines will take place at one of the testing grounds. This event will demonstrate the potential of the competition projects and help refine future plans.
The 5,56×45mm M855A1 cartridge and its bullet
The Special Operations Command has not yet specified how long the HICAR project will last, what funding will be allocated, etc. However, it is already clear that the project could take several years and cost at least millions of dollars.
New cartridge
The key element of the HICAR program is the M855A1+ intermediate cartridge. It is based on the existing M855A1 Enhanced Performance Round and features a number of improvements that enhance key performance characteristics.
The new M855A1+ cartridge retains the standard 5,56×45mm ammunition geometry. It features a metal case with a reinforced propellant charge. It uses the bullet from the previous EPR cartridge. It is made of copper and has a steel armor-piercing core. This bullet is lead-free, reducing the health risks to military personnel and the environment. The total bullet weight is 4 grams, and the core weight is 1,2 grams.
The "plus" cartridge features a reinforced propellant charge based on a new grade of propellant powder. According to available data, this increases peak gas pressure to 82 psi (approximately 5650 bar)—versus approximately 65 psi (approximately 4275 bar) for the EPR cartridge. These values significantly exceed the standard pressure for 5,56mm ammunition and require verification, but their magnitude alone indicates the extreme nature of the ammunition for this caliber.
The exact combat characteristics of the M855A1+ cartridge have not yet been disclosed. According to various estimates, with a 12-inch barrel, it will increase the muzzle velocity to 950–1000 m/s. Other parameters are expected to improve as well. Most importantly, the effective range against armored targets will increase to 600 m, a level the standard M855 can only achieve against unarmored targets. This compensates for the range penalty imposed by modern personal protective equipment.
Enhanced receiver
The main objective of the HICAR program is to adapt the M4A1 carbine to the M855A1+ cartridge, with all its features. USSOCOM outlined the basic principles of this work in published documentation.
Participants in the program will be required to develop a new receiver (the so-called upper receiver) and barrel that meet the cartridge's specifications. Essentially, this is a refinement of the standard Upper Receiver Group - Improved (URG-I) product. An updated bolt with the appropriate strength specifications is also required.
The new receiver must retain standard dimensions and components. It must be fully compatible with the so-called lower receivers of the M4A1 carbine in its current form. External rail interfaces must be present for the installation of additional devices.
The HICAR receiver is designed to be equipped with a rifled barrel 11-12 inches (279-305 mm) long. The barrel shank will be subject to increased stress, requiring its strength. The muzzle is planned to be fitted with the standard USSOCOM HUXWRX Flow 556k suppressor (the model name should be verified separately).
The customer strictly limited the dimensions and weight of the carbine after modernization:
- maximum length - 31 inches (787 mm);
- desired length - 28 inches (711 mm);
- maximum weight (without cartridges and additional devices) - 8 pounds (3,6 kg);
- desired weight: 6,5 lbs (2,95 kg).
For comparison, the production M4A1 weighs around 3,4 kg, so the desired 2,95 kg with a significantly reinforced structure is a truly challenging bar.
The requirements for reliability and service life are also strict:
- minimum barrel life is 8 thousand shots;
- desired resource - 20 thousand shots;
- at least 800 shots between delays;
- at least 5 thousand shots between failures;
- operational range from -40 °C to +74 °C;
- the ability to fire after being caught in snow, sea water, dust, etc.
The introduction of a new cartridge does not preclude the use of existing ones. M4 HICAR rifles are designed to use the full range of existing 5,56mm cartridges, such as the M855 (both versions) and the Mk 262.
Design tasks
The HICAR program participants face complex challenges. While individual modernization requirements are easily achievable, integrating the entire technical specifications will be challenging. Designers will have to find new technical solutions, technologies, and materials while remaining within the original M4A1 architecture.
Essentially, the project's main goal is to increase the strength of the rifle's key components. This is a complex issue and affects all elements of the prospective receiver, so virtually every component will have to be redesigned.
The reinforced M855A1+ cartridge increases bore stress and wear. It also impacts the durability of direct impingement gas-operated systems. This design vents propellant gases directly into the bolt carrier, making it more sensitive to excess impulse than piston-operated systems. The loads on the bolt carrier and buffer will increase, and the receiver will have to withstand more powerful impacts.
An obvious solution to some of these problems would be to simply increase the thickness of the components: this would improve their resistance to mechanical and thermal stress. However, size and weight limits effectively preclude thickening the barrel or receiver. Designers will have to seek other solutions—new metals and alloys, component coating options, and different component configurations. At the same time, the "upper receiver" cannot incorporate significant innovations and must retain its original features.
This is where the program's main risk lies. A sharp increase in pressure directly conflicts with the requirement for a service life of 8–20 shots: the higher the pressure and wear, the more difficult it is to ensure the longevity of the barrel and automatics. Whether the entire set of requirements can be met with the stated cartridge parameters remains an open question.
The deadlines are also tight. Participants are given only a few weeks to evaluate their capabilities and prepare documentation, and two and a half months from the date of receipt of the order to develop and manufacture the prototype weapon.
Yet, upgrading an existing carbine remains simpler, faster, and cheaper than creating a new system from scratch based on the NGSW—that's the rationale behind USSOCOM's choice. The real intrigue lies elsewhere: will the contractors be able to meet the strict weight, service life, and reliability limits with such high pressures for the 5,56 caliber? The answer to this question will determine the fate of the entire program.
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