The Colt IAR6940 (Infantry Automatic Rifle)

By Christopher R. Bartocci

On 27 March 2008, the U.S. Marine Corps submitted a Purchase Description for the Infantry Automatic Rifle (IAR) to the industry. The Marines were seeking designs which would fit very specific parameters. The purpose of the IAR is to replace the M249 Squad Automatic Weapon (SAW) with an automatic rifle easily manned by a single infantry marine that has emphasis on light weight and portability in order to maximize dismounted maneuverability. The feelings throughout the Marine infantry community are mixed on the concept of the IAR. Some feel the M249 is the center of the unit’s firepower and the belt fed capability is essential to get out heavy volumes of firepower. Others believe a lighter, more reliable magazine-fed weapon will increase maneuverability, accuracy and mobility. Having a magazine fed weapon utilizing the proven M16/M4 magazine would also create better commonality and reliability in the IAR. The magazine feed system on the SAW has been mediocre at best in the area of reliability.

The Marines specified the kit which would accompany the IAR. This included the Matech BUIS (NSN 1005-01-541-1772), Blank Firing Adapter, Grip Pod™ (NSN 1005-01541-1712), three point sling (NSN 8465-01-524-8847), cleaning kit, operators manual and sufficient magazines to hold 300 rounds of 5.56x45mm NATO ammunition.

Performance characteristics including the IAR must weigh less than 12.5 pounds with the Grip Pod™ and BUIS attached. The IAR shall be less than 40 inches in length and demonstrate less than 4 MOA dispersion in automatic fire. Precision automatic fire is required and to demonstrate less than 8 MOA with 5 round bursts. The probability of hit should be a minimum of 2 rounds from a 5 round burst onto an “E” silhouette at 50 meters 70% of the time within 3 seconds of target exposure. The rate of fire of the IAR must be capable of 36 rounds per minute for 16 minutes and 40 seconds without a barrel change or cook-off of the round in the chamber or magazine. The weapon is to have both semi and fully automatic modes of fire and be finished in Coyote Tan. Other features include a four position stock and a handguard to protect the shooter’s hands from heat. Interface requirements required compatibility with the full range of U.S. issue 5.56mm ammunition and use the standard M16/M4 magazine. The IAR must use Mil-STD-1913 dimension rails and a BUIS. The IAR must also be able to mount the standard Marine Corps Multi-Purpose Bayonet (NSN 1095-01-506-3424).

Developmental contracts were awarded to Colt Defense, FN Manufacturing Inc and Heckler & Koch.

Colt Defense was awarded developmental contracts for two of their entries, the IAR6940 and the IAR6940H.

Colt Infantry Automatic Rifle: IAR6940

The Colt IAR6960 is a lightweight, gas operated, magazine fed, 5.56x45mm caliber automatic rifle. The IAR is based on the time tested and combat proven M16/M4 series rifles. The IAR incorporates the same safety features and human engineering features as the M16/M4 series of weapons.

The upper receiver is made with Colt’s 1-piece upper receiver (actually two pieces due to the bottom handguard being removable) which offers several enhancements to the weapon. A full length top rail spans from the charging handle to the front sight base. Quad MIL-STD-1913 rails permit any comprehensible accessory to be mounted with ease. The one-piece upper receiver provides complete zero retention for mounting optics. The barrel is held by an improved barrel nut offering more bearing surface for a tighter fit. The upper receiver incorporates the forward assist assembly, fired cartridge case deflector and closing ejection port cover. Multiple air ventilation holes are in the forward portion of the receiver to permit more rapid cooling. The receiver is also equipped with the standard GI issue Matech back up iron sight.

The barrel is a heavy 16.1 inch barrel. Extending the length from 14.5 inches was needed to provide the longer range requirements required of the Infantry Automatic Weapon. The barrel is chrome plated with the GI 1 turn in 7 inch rifling twist which permits the rifle to accurately fire the full range of 5.56mm ammunition from M855 ball to the 77 grain Mk262 Mod 0 cartridge. Pinned to the barrel is a bayonet stud which permits the bayonet to be mounted on the longer barrel. Mounted to the barrel is the front sight base/gas block which has Colt’s new folding front sight. With the sight folded, the shooter gets the full field of view with an optic. The sight flips up and down by detent so there is no locking lever or button that must be pushed. On the current production models, the front sight is equipped with a sliding lock that was brought about by request of the customer. Currently all Colt folding front sights are equipped with the new lock. The standard M4/M16 compensator is used which is very effective for suppressing muzzle flash. Attached to the barrel is a unique Colt designed heat sink which increases cook-off time during extended periods of fire. The heat sink draws heat out of the barrel permitting quicker cooling. Another benefit is the heavy barrel extends the life of the barrel over standard rifle lightweight rifle barrels. Attached to the upper receiver is a lower rail which is removed by removing two screws and pulling the latch down and sliding the rail off. To protect the shooter’s hand from heat is a handguard which attaches to the lower rail. Normally that will be removed in favor of the Grip Pod™.

The bolt carrier group is the standard M4 bolt carrier group. Equipped with the heavy extractor spring the bolt carrier group provides no logistical burden for repair or replacement parts. The charging handle assembly is also standard for the M4/M16 weapon system.

The lower receiver as per the requirements has several changes made. The standard 4-position receiver extension is used with the VLTOR E-Mod stock. This enhanced stock is the “clubfoot” design which provides a place to hold with the non firing hand while firing in automatic, The shape of the cheek weld is triangular, which is more comfortable compared to the traditional GI stock. Provided in the cheek weld (both sides) are battery storage compartments which are water resistant. An additional compartment is located on the left side of the rear of the stock which can take batteries or spare part. Basically whatever you can fit in it! There are quick detachable sling swivel mounts on both sides of the stock. Also attached is a heavy duty rubber buttplate. Based on testing, the E-Mod stock stood up to and passed all the grueling drop tests without breaking making it one of if not the most durable stocks in the industry. Additionally Colt uses a new buffer for the IAR, the H3. This extremely heavy buffer is made of three heavy tungsten weights. This buffer is necessary to make this weapon fire reliably is all climates and conditions due to the operating dynamics
of the barrel.

The trigger group is the standard selective fire group. The main difference is that it has an ambidextrous selector lever. The handle on the right is significantly shorter than that of the left. This is so it does not obstruct the trigger finger of the shooter. Additionally the lower receiver is equipped with the Norgon ambidextrous magazine release. This magazine release is equally as useful for a right hand shooter. The left hand can pull the magazine out and depress the mag release with the thumb in one quick motion. The weapons sent for testing for the Marine Corps were all colored in Coyote Tan while LE/EXPORT models are all black.

The overall length of the IAR is 36.75 inches with the stock extended and 33.50 inches closed compared to the 41 inch long SAW. The weight of the IAR is a light 9 lbs 8.oz compared to the 17 pound M249 SAW. The cycle rate of the IAR is 700 to 1000 rounds per minute which is comparable to the M249 SAW. With the IAR’s 16.1 inch barrel, the muzzle velocity with M855 Ball ammunition is 2920 feet per second compared to the 21 inch barrel of the M249 SAW with a muzzle velocity of 3000 feet per second.

Instead of the standard GI aluminum magazine, the IAR comes with the MagPul manufactured PMag. The PMag offers a significant reliability enhancement over the current aluminum magazine in both feeding reliability as well as durability. Testing shows the PMag maintains better control of the cartridge during the feeding process as well as the cartridge strips much smoother. The shape of the magazine enhances feed reliability by its constant curve construction. This means the cartridges sit in the magazine in their natural state rather than sit in a magazine which has two separate bends in it. Additionally the PMag has an anti-tilt follower which also prevents feed problems with the nose of the projectile being pushed into the front of the magazine and stalling. The durability of the polymer used is amazing. During testing of the PMag in previous articles I had run over the magazine numerous times with my Dodge Durango. Picked up the magazine and put it in a Colt M4 and fired all 30 rounds on auto with no malfunctions. Additionally this author froze 6 of the magazines and subjected them to drop and function checked with 100% reliability. Also solvent and water submersion tests were conducted with no ill affect toward the magazine. Another benefit is the Maglevel system which provides two windows in the magazine to allow the shooter to know approximately how many rounds are in the magazine.

The Grip Pod™ is certainly worth mentioning. This outstanding vertical pistol grip/bipod has gained acceptance by the Marine Corps for all of their rifles. The Grip Pod with a push of a button deploys a bipod from the base of the grip. When in the prone position the Grip Pod sits up high enough that the 30 round magazine will not interfere with aiming of the weapon. The strength of the Grip Pod is very respectable. One can stand on top of the barrel and the Grip Pod would not break, it would support the weight. The convenience of having this feature increases effectiveness as well as accuracy in a split second.

Firing Impressions

The optic chosen was an AimPoint Comp 4 reflex sight which was battle sight zeroed at 25 yards. There were pop up target out to 400 yards. The ammunition selected for firing was M855 NATO ammunition. The magazines chosen were both the PMag as well as the 100 round BETA C-Mag. More than 2000 rounds were fired throughout the evaluation. No mechanical malfunctions were encountered whatsoever. The rifle was fired single shot, short bursts and continuous bursts of automatic fire. Targets were steel silhouettes at 50, 100, 150 and 200 yards.

Due to the weight, Grip Pod and the shape of the stock the IAR was deadly accurate. While firing burst the rifle hardly moved. There was no problem firing off 10 to 20 round bursts and hitting center mass of a 50 yard silhouette target. On the reactive target range the IAR was placed on automatic fire. Firing short bursts (3 to 5 rounds) there was no difficulty hitting 25 to 200 yard targets. The 250 and 300 yard targets were also engaged but not as consistently as the 200 and below range. With the rifle placed in the semi-automatic mode and the optic changed to an ELCAN 4x20 scope, the 300 yard targets were consistently engaged. The IAR has gone through some very rigorous testing which was what the IAR program was all about. They wanted a sustained fire weapon, the Colt IAR was just that. Testing showed the IAR would go through more than 1,000 rounds continuous without failure. The combination of the heavy barrel and heat sink increased the operational parameters significantly over the M4A1. The M4A1 with SOCOM heavy barrel continuously fires around 870 rounds to failure. These numbers are outstanding for a non belt fed machinegun without a replaceable barrel in the field.

Colt Infantry Automatic Rifle: IAR6940H

The second entry Colt submitted was the IAR6940H. This was done jointly with Knight’s Armament Company. The specifications are very similar to the standard IAR6940 but the H utilized a KAC designed and manufactured heat sink, handguard and KAC back up rear sight. Like the IAR6940, the handguard assembly could not be removed for maintenance or to have a barrel change. All IAR models, you would replace the complete upper if you were to have shot out the barrel. Also the KAC heat sink and handguard was far more complex than the Colt and was much more difficult to assemble.

This model was not test fired for the purpose of this article. The model was dropped by Colt following the conclusion of the IAR trial by the Marine Corps.

There was actually a third Colt IAR model called the IAR6940P but this rifle was not submitted in the end by Colt. This was an IAR6940H with the only difference being it was not a direct gas impingement rifle but an external piston. The operating system was basically that of the never produced LE1020. There was never any real explanation as to why the piston operated model was not submitted. It is the opinion of this author that there would have been no mechanical benefit to it over the direct gas. The durability shown by the IAR6940 was exceptional. The rifle never failed in testing due to any “fouling” caused by the direct gas impingement system.

The IAR6940 has gone on to be a solid member of the Colt LE and military product lineup. It fills a very specific role that nothing else in the Colt lineup will do. It is not designed as a lightweight infantry carbine but an assault rifle that will fill the need of a light support weapon without looking very conspicuous as someone carrying an M249 SAW would. Sales of the IAR6940 have been made to Mexico for use by their Marines engaged in fighting the war on drugs. In the end, the contract went to Heckler & Koch for an IAR based on their HK416. The IAR program has been controversial to say the least. Not necessarily the final rifles tested and adopted but the concept of having a magazine fed weapon replace a belt fed one. Some believe that switching to a magazine fed rifle is a downgrade in the unit’s firepower. Others believe it is better due to only having to carry magazines compatible in all infantry weapons as well as the look of the rifle will not draw as much attention as a SAW would for snipers and so on. The two sides still fight about that to this day. But the M27 IAR has seen combat and is in use by the Marines. The Colt IAR is serving in numerous other places throughout the world and remains a popular military rifle.

This article first appeared in Small Arms Review V20N8 (October 2016)
and was posted online on August 19, 2016


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