Geissele Hypervelocity Improved Capability Assault Rifle

History

The Geissele Hypervelocity Improved Capability Assault Rifle, abbreviated HICAR, is a 5.56 mm M4-style rifle developed by Geissele Automatics in response to a U.S. Special Operations Command requirement for a weapon capable of using future hypervelocity ammunition.

The program is intended to extend the capabilities of the legacy M4 carbine. The Naval Surface Warfare Center solicitation called for an M4-style platform able to fire future hypervelocity 5.56 mm ammunition and increase effective range from about 300 m to 600 m.

Geissele presented the HICAR in 2026 as a production-ready design, although high-round-count durability testing was still continuing and the rifle had not reached its final iteration.

Development

The Naval Surface Warfare Center issued the solicitation in May 2026 with a 21-day response period. Geissele Automatics was able to respond quickly because the company had already worked for about three years on government and commercial projects involving high-pressure ammunition.

According to company founder and president Bill Geissele, the HICAR was already beyond the prototype stage by September 2026 and could enter manufacturing if an order was received. At the same time, he emphasized that endurance testing remained incomplete, particularly testing of barrel life under the substantially greater pressures produced by the new ammunition.

The U.S. military hypervelocity 5.56 mm ammunition associated with the requirement was identified in the source as M855A1+. U.S. Army Combat Capabilities Development Command described it as a conceptual approach for obtaining increased range and performance within an existing caliber. Detailed military cartridge specifications were not disclosed.

Testing

For internal testing and demonstrations, Geissele developed its own hypervelocity cartridge from commercially available components to replicate the intended military ammunition. Bill Geissele stated that the test cartridge operated at approximately 565 MPa (82,000 psi), about 20,000 psi above the pressure of the legacy 5.56 mm ammunition used for comparison.

Geissele engineers tested the rifle with chronographs and long-range optics while monitoring velocity, accuracy and component wear. A demonstrated configuration with a 292 mm (11.5 in) barrel and a 5.0 g (77-grain) projectile was reported by the company to produce a consistent muzzle velocity of approximately 823 m/s (2,700 ft/s). Geissele also claimed accuracy to 800 m with this configuration. This company demonstration claim is separate from the Naval Surface Warfare Center requirement for an effective range of 600 m.

Testing focused heavily on material wear because high-pressure ammunition imposes increased mechanical and thermal stress on the barrel. Geissele said thousands of rounds were required to evaluate performance and wear, but the first barrel iteration had not yet accumulated enough rounds to establish its ultimate service life.

Additional information about the program was reported by Military Times.

Design

The HICAR follows an M4-style configuration and is specifically engineered to tolerate substantially higher ammunition pressure than conventional 5.56 mm weapons. The source does not provide complete dimensions, weight, operating-system details or magazine specifications.

Barrel and pressure resistance

One of the principal engineering challenges is the increased stress imposed on the barrel by hypervelocity ammunition. Geissele therefore selected a higher-grade steel described by the company as a type normally reserved for artillery barrels. The design is intended to withstand the greater pressure while maintaining useful accuracy and component life.

The company was still evaluating barrel longevity in September 2026. Consequently, a final barrel service-life figure had not been established and the production configuration remained subject to further refinement.

Ammunition

The HICAR was developed around future high-pressure 5.56 mm ammunition rather than a larger-caliber cartridge. The military ammunition was described as M855A1+, but detailed specifications were not publicly available in the supplied source.

Geissele's demonstration ammunition was loaded to approximately 565 MPa (82,000 psi). The company used this ammunition to reproduce the pressure and performance expected from the military hypervelocity concept during development testing.

Geissele stated that a civilian version of the HICAR would not be offered until suitable hypervelocity ammunition became commercially available.

Program status

As of September 2026, Geissele described the HICAR as production-ready and beyond the prototype phase. The company said it could begin manufacturing rifles if it received an order. However, testing was still underway and the design had not reached its final iteration because extremely high round-count endurance testing had not been completed.

The supplied material does not confirm a production contract for HICAR rifles, formal adoption by SOCOM, a fielding date or an operational unit. The rifle should therefore be regarded as a developed and production-ready candidate for the SOCOM requirement rather than an operational service weapon.

Specifications (HICAR 11.5-inch demonstration configuration)

General characteristics

• Type: Assault rifle
• Manufacturer: Geissele Automatics
• Caliber: 5.56 mm
• Configuration: M4-style platform
• Barrel length: 292 mm (11.5 in)
• Development ammunition: Geissele high-pressure 5.56 mm demonstration cartridge intended to replicate the military hypervelocity concept
• Projectile mass in demonstrated configuration: approximately 5.0 g (77 grains)
• Demonstration ammunition pressure: approximately 565 MPa (82,000 psi)

Performance

• Muzzle velocity: approximately 823 m/s (2,700 ft/s) with the 292 mm barrel and 77-grain projectile, according to Geissele
• SOCOM solicitation effective-range objective: 600 m
• Company-reported demonstration accuracy: out to 800 m