Born from the rigorous demands of the USMC Infantry Automatic Rifle program, the Colt IAR 11.5" Monolithic Upper Receiver Group represents a sophisticated evolution in AR-platform engineering. This complete upper assembly combines Colt's renowned manufacturing precision with innovative thermal management solutions developed jointly with Knights Armament Company.
The foundation of this system is Colt's monolithic upper receiver, distinguished by its Cerro forge "C" marking and precision-machined continuous top rail. This uninterrupted rail platform provides superior optical mounting stability while facilitating the integration of the free-floated barrel system. The upper features crisp, white laser-etched "T" markings for consistent accessory placement.
At the heart of this assembly is the IAR-specific heavy profile 11.5" barrel. Chrome-lined for enhanced durability and heat resistance, this barrel configuration was engineered specifically to address the sustained fire requirements of the automatic rifle role. When paired with the innovative KAC heat guard system (P/N: 25714), testing demonstrated a remarkable 30-40% improvement in sustained automatic fire capability compared to the standard M4A1 platform.
The integrated gas block design incorporates a folding front sight, complemented by an included Matech rear backup iron sight. This sight configuration maintains compatibility with modern optics while ensuring reliable backup sighting solutions. The gas block's positioning and engineering contribute to the system's reliability under intensive use conditions.
This upper receiver group represents a pivotal moment in modern infantry doctrine. The IAR (Infantry Automatic Rifle) program emerged from the USMC's revolutionary concept to replace the belt-fed M249 Squad Automatic Weapon (SAW) with a magazine-fed automatic rifle platform. This shift aimed to transform every squad member into a potential automatic rifleman while maintaining the sustained fire capability traditionally provided by belt-fed weapons.
The joint Colt/KAC 6940H IAR submission addressed this challenge through innovative engineering. The heavy barrel profile between the chamber and gas block, combined with the aluminum heatsink handguard, achieved approximately 30-40% greater sustained automatic fire capability compared to the standard M4A1. This improved heat management proved crucial for the automatic rifle role, allowing extended firing periods while maintaining accuracy and reliability.
While the USMC ultimately selected the HK 416 platform (designated M27 IAR) for general service, this Colt IAR variant found its niche among specialized units, including FBI HRT, who sought similar capabilities in a more compact package. The 11.5" configuration offered here represents the synthesis of these requirements - combining sustained fire capability with maneuverability.
This upper receiver group is presented in anodized black, and is a contract over-run, made available direct from Colt. The contract might have been FBI or foreign military. While this is the black anodized model, we do hope to also have the FDE colored model that was part of the USMC submission, while keeping with the shorter 11.5" barrel. This upper should be paired with a military grade forged AR15/M4 lower receiver. For obvious reasons, Colt is probably your first choice, but LMT, Knights and FN will also be suitable lowers.
As far as design, it is not hard to think of this as a monolithic 11.5", like LE6945, which, really is part of this upper. A large heatsink is implemented on the lower hand guard, which is aimed to increase the time it takes for the firearm to cook-off under extended periods of fire due to overheating. It can be replaced or equipped with grip attachments. Also, the barrel is not your M4 Government profile. This barrel was meant to serve up machine gun fire, so is thicker than a SOCOM barrel. Good thing it is chrome-lined, as we are not sure where you will get a replacement if you burn it out, but that will be 20,000 rounds later.
Potomac Armory
