Authoritative military publication dedicated to light weapons
The civilian version of the IAR6940H rifle equipped with KAC handguards has different handguard length and gas block shape compared to the IAR6940H rifle
The bidding proposal for the Infantry Automatic Rifle (hereinafter referred to as IAR) released by the US Marine Corps aims to meet a series of specific criteria. The purpose of the IAR is to replace the M249 Squad Automatic Weapon (SAW), which can be operated by a single Marine, and is lighter and easier to carry, maximizing weapon mobility when not set up with a bipod.
Marines have different opinions about the concept of the IAR. Some believe that the M249 SAW is the firepower core of the squad, and the belt-fed capability is essential for providing strong fire support. Others think that a lighter and more reliable magazine-fed weapon can improve operability, mobility, and shooting accuracy. Additionally, if the IAR uses magazines compatible with the current M16/M4, it can enhance its versatility and reliability, and using a rifle-like IAR can reduce the chances of infantry providing fire support being prioritized for elimination by enemy snipers.
The Marine Corps specifically outlined the accessories used on the IAR, including Matech backup iron sights, blank-firing adapters, grip-style bipods, three-point slings, cleaning tools, and sufficient magazines to carry 300 rounds of 5.56×45mm NATO standard ammunition.
With the grip-style bipod and backup iron sights installed, the weight of the IAR must be less than 12.5 pounds (5.67 kg), and the overall length must be shorter than 40 inches (1016 mm). For accurate full-auto shooting, the five-shot burst accuracy must be less than 8 MOA. The hit rate requirement: during a 3-second exposure of a half-body silhouette target at 50 meters, at least 3 out of 5 shots must hit.
The combat rate of fire must reach 36 rounds per minute, sustained for 16 minutes and 40 seconds. The weapon must have semi-automatic and full-automatic firing capabilities, along with features including a 4-position adjustable telescoping stock and a heat shield to protect the shooter’s hand from burns.
Versatility requirements include the ability to use all standard US military 5.56mm ammunition, with the feeding mechanism utilizing standard M16/M4 magazines. Additionally, it must have MIL-STD-1913 rails for mounting backup iron sights. The IAR must also be compatible with the Marine Corps’ standard multipurpose bayonet (NSN 1095-01-506-3424, NSN is the NATO Stock Number).
Colt, FN, and HK participated in this bidding, with Colt providing the IAR6940 and IAR6940H rifles.
IAR bidding participants: Colt IAR6940 rifle
Colt IAR6940 rifle specifications
The Colt IAR6940 automatic rifle is chambered in 5.56×45mm, operates on a gas-operated (direct impingement) automatic principle, and uses a magazine-fed system, making it relatively lightweight. This rifle is developed based on the battle-tested M16/M4 series, thus its safety operation method and ergonomic design are identical to those of the M16/M4.
When fully extended, the Colt IAR6940 rifle measures 933mm in length, and when the stock is not extended, it measures 851mm, while the M249 SAW measures 1041mm in length. The total weight of the IAR6940 rifle is 4.31kg, while the M249 SAW weighs 7.71kg. Additionally, the theoretical rate of fire for the IAR6940 rifle is 700-1000 rounds per minute, which is similar to that of the M249 SAW (due to the magazine-fed system, the combat rate of fire for the IAR6940 is lower than that of the M249 SAW, resulting in less suppressive capability). When firing M855 ammunition, the IAR6940 rifle has a barrel length of 409mm and an initial velocity of 890m/s, while the M249 SAW has a barrel length of 521mm and an initial velocity of 914m/s.
The Colt IAR6940 rifle mainly consists of the barrel assembly, bolt/bolt carrier assembly, upper receiver assembly, lower receiver assembly, feeding mechanism, and grip-style bipod.
Close-up of the Colt IAR6940 rifle with grip-style bipod installed
The export version of the Colt IAR6940 rifle features a black appearance
Close-up of the folding front sight and bayonet mount of the Colt IAR6940 rifle export model
Barrel assembly
The barrel of the Colt IAR6940 rifle is 409mm long; the reason for extending the M4 carbine’s 368mm barrel to 409mm is due to the need for a longer effective range in an infantry automatic rifle.
It uses a heavy barrel, which has a longer lifespan compared to standard rifle barrels. The barrel is chrome-lined, with a twist rate of 178mm as per military standards. This twist rate allows for accurate shooting of most 5.56mm ammunition, from M855 to MK262 MOD0. The barrel also features a fixed pin to secure the bayonet mount.
The integrated front sight/gas block mounted on the barrel is a newly developed foldable sight/gas block by Colt. When the sight is folded down, the shooter can achieve a complete field of view when using optical sights. The folding and raising of the sight is positioned by a spring locator, eliminating the need to push any locking levers or press buttons.
The muzzle device is a standard birdcage flash suppressor used on the M4, effectively eliminating muzzle flash. The barrel is equipped with Colt’s designed heat sink, which helps delay overheating during sustained fire.
The bolt/bolt carrier assembly and charging handle are standard M4/M16 components, while the extractor spring uses a higher performance extractor spring with greater elasticity. The high-strength extractor spring can increase its lifespan, reduce the need for replacements or repairs, thus alleviating logistical pressure.
The upper receiver is manufactured by Colt, with the top rail extending from the front of the charging handle to the front sight position, and standard Matech backup iron sights mounted on the top rail. The left and right sides and bottom of the handguard also have rails, allowing for the easy installation of various accessories.
By unscrewing the screws on the lower handguard, the lower handguard can be removed. After removing the lower handguard, a large heat sink connected to the upper receiver can be seen, with many ventilation holes to increase air circulation, improve heat dissipation efficiency, and effectively delay barrel overheating.
The lower handguard is secured to the upper receiver with screws, and can be removed by unscrewing the screws. After removing the lower handguard, a large heat sink connected to the upper receiver can be seen, with many ventilation holes to increase air circulation, improve heat dissipation efficiency, and effectively delay barrel overheating.
To protect the shooter’s hand from burns, when no accessories are mounted, heat-resistant covers can be installed on the lower rail and left/right rails, and when accessories are needed, the heat-resistant covers can be removed.
The upper receiver also features an auxiliary charging handle, a dust cover for the ejection port, and a cover for the dust cover.
To meet requirements, the lower receiver underwent some modifications. The stock uses the VLTOR EMOD (Enhanced Modular) stock, which has passed all drop tests conducted by the Marine Corps and shows no damage, making it one of the sturdiest AR stocks available.
Colt IAR6940 rifle export model with H3 buffer
Left side close-up of the Colt IAR6940 rifle export model, note the inscription “CLOT IAR”, featuring dual-sided magazine release designed by Norgon
Lower receiver of the Colt IAR6940 rifle export model, featuring dual-sided fire selector. Since its lower receiver is basically the same as the standard M4A1 carbine lower receiver, only minimal modifications are needed to convert an M4A1 lower receiver to an IAR6940 lower receiver.
The stock features waterproof storage compartments on both sides, with covers that can store batteries.
Close-up of the storage compartment cover located at the lower back of the stock in a closed state
The storage compartment at the lower back of the stock can be opened from the left side, allowing for storage of batteries or other spare parts.
The EMOD stock features a “clubfoot” design, which allows the shooter to grip the stock with their non-firing hand during full-auto fire. The stock’s cheekrest is triangular, providing more comfortable aiming compared to the standard Army enhanced stock. The stock features waterproof storage compartments on both sides, with covers that can store batteries. Additionally, there is a storage compartment at the lower back, which can be opened from the left side to store batteries or other spare parts. The stock has mounting holes for quick-release sling swivels on both sides. The rear of the stock can also accommodate a thicker rubber recoil pad.
Colt has employed a new H3 buffer in the IAR. This buffer is heavier and filled with three tungsten weights, allowing the weapon to operate reliably in various environments (the three tungsten weights generate sufficient forward momentum due to inertia when the bolt carrier returns to position, preventing bolt bounce).
It uses a standard full-auto/semi-auto trigger. The fire selector lever is positioned on both sides of the lower receiver, with the right side lever being shorter, ensuring it does not interfere with the shooter’s trigger finger.
The lower receiver features a dual-sided magazine release designed by Norgon. This magazine release allows both right-handed and left-handed shooters to use it easily; right-handed shooters can press the left magazine release with their left thumb while removing the magazine.
The IAR6940 rifle does not use military-standard aluminum magazines for feeding; it uses PMAG magazines manufactured by Magpul. In terms of feeding reliability and magazine durability, PMAGs are superior to standard aluminum magazines. Tests have shown that PMAGs exhibit better control over ammunition during feeding, and the ammunition exits the feed lips more smoothly. The curved shape of the PMAG also enhances feeding reliability.
The PMAG’s follower features an “anti-tilt” design, addressing issues with uneven pressure that can cause excessive wobble. Additionally, the PMAG is made of polymer material, which offers high strength. It is said that some individuals have frozen six PMAGs and conducted drop tests on them, and these magazines maintained high reliability.
The grip-style bipod is a controversial accessory.
Some believe that the grip-style bipod is one of the best accessories for the Marine Corps. It can be extended from the bottom of the grip by simply pressing a button, and when shooting from a prone position, the grip-style bipod supports the rifle, preventing the 30-round magazine from affecting aiming. The grip-style bipod is also quite strong; a person can even stand on the barrel without breaking it.
Another viewpoint is that the grip-style bipod is too large as a grip, and its mounting position is often limited. In use, there is a dilemma: as a grip, its mounting position is too far back, making it unsuitable for bipod use; if it is to fully utilize the bipod function, its mounting position needs to be further forward, which then makes it unsuitable as a grip. Additionally, its strength does not match that of the M249 SAW’s bipod.
So how effective is this grip-style bipod? The author believes that it is necessary to examine the currently used M27 IAR to observe the prevalence of the grip-style bipod within the Marine Corps and the feedback from Marines.
IAR6940H rifle with KAC SR-16 carbine lower receiver installed
The IAR6940H rifle is another Colt prototype participating in the IAR bidding, jointly manufactured by Colt and KAC. The specifications of the IAR6940H rifle are similar to those of the standard IAR6940 rifle, but the IAR6940H rifle utilizes heat sinks, handguard covers, and backup iron sights manufactured by KAC.
Like the IAR6940 rifle, the handguard cover of the IAR6940H rifle is detachable. Additionally, KAC’s heat sinks and handguard covers are more complex and difficult to install compared to Colt’s.
The handguards produced by KAC for the IAR6940H are different from the standard IAR6940 handguards, and the heat sink is not fixed to the barrel but is integrated with the lower half of the handguard
The lower half of the handguard of the IAR6940H rifle is secured to the rear of the barrel by two screws
The design of the handguard for the IAR6940H rifle is very unique. The handguard is divided into two parts, with the lower half secured to the rear of the barrel by two screws, and the upper half fixed to the lower handguard with four screws, thus securing the handguard to the barrel. In this structure, the weight of the handguard is completely borne by the barrel. While this force may have some impact on the barrel, the location of the force is at the rear of the barrel, so the impact may not be as significant as expected.
The heat sink and lower half of the handguard are designed as a single unit, with some openings to improve heat dissipation efficiency.
Currently, a small number of Colt IAR export models are still in service with the Mexican Marine Corps, and these Colt IARs have a black appearance.
Below are some testing results from that year.
Testing Method: Three rifles of each model were taken, and each rifle fired 20,000 rounds at a rate of 30 rounds per minute. After firing 120 rounds, the weapon was cooled, and after firing 600 rounds, maintenance was performed; after firing 1200 rounds, a technical inspection was conducted to assess barrel wear.
Requirements: The interval for experiencing level 1 or 2 malfunctions must be 900 rounds, and the interval for experiencing level 3 malfunctions must be 15,000 rounds (Note: Level 1 malfunction is one that the shooter can immediately clear. Level 2 malfunction requires the shooter to spend 10 seconds to 10 minutes to clear, and the tools to resolve the malfunction must be those provided with the weapon. Level 3 malfunction requires more than 10 minutes to clear, necessitating two or more individuals to resolve, or requiring a specialist using tools not provided with the weapon).
Testing Results: Colt’s 09A prototype (test number 09A) averaged 952 rounds fired before experiencing a level 1/2 malfunction, and averaged 60,000 rounds before experiencing a level 3 malfunction, estimating its barrel life at 1800 rounds.
Colt’s 09B prototype averaged 1277 rounds fired before experiencing a level 1/2 malfunction and averaged 15,000 rounds before experiencing a level 3 malfunction, estimating its barrel life at 1400 rounds.
FN’s 09C prototype averaged 5000 rounds fired before experiencing a level 1/2 malfunction, with no level 3 malfunctions occurring during the testing, estimating its barrel life at 5200 rounds.
HK’s 09D prototype averaged 1622 rounds fired before experiencing a level 1/2 malfunction and averaged 20,000 rounds before experiencing a level 3 malfunction, estimating its barrel life at 16200 rounds.
Both Colt and FN prototypes exhibited relatively low barrel life, particularly Colt’s prototype, which had an unusually low barrel life, raising questions about the assessment method used.
High and Low Temperature Reliability Testing (2008)
Testing Method: Three rifles of each prototype were taken, and the selected rifles were placed at specified temperatures for at least 4 hours to reach the required temperature. Each of the three rifles fired 1800 rounds at a normal temperature of 25±8℃, 300 rounds at a cold temperature of -32℃, and 300 rounds at a high temperature of 71℃. The firing rate was 30 rounds per minute, totaling 2400 rounds per rifle, and 3 rifles fired a total of 7200 rounds. During the firing process, a certain number of rounds were allowed for cooling and lubrication of the weapon.
Testing Results: Colt’s A prototype experienced 60 malfunctions, Colt’s B prototype experienced 28 malfunctions, HK’s G prototype experienced 27 malfunctions, and FN’s J prototype experienced 26 malfunctions.
Detailed results of the accuracy testing are currently unavailable. It is reported that HK’s prototype had the highest shooting accuracy, followed by FN’s prototype. After all, Colt’s prototype had a large heat sink fixed to the barrel, which could significantly affect shooting accuracy.
Users firing the Colt IAR6940 rifle with live ammunition, equipped with an Aimpoint Comp M4 reflex sight, had a zeroing distance of 25 yards (1 yard = 0.914m). The NATO standard M855 ammunition was used, with feeding mechanisms including 30-round PMAG magazines and 100-round BETA C-MAG drums. The farthest shooting target was at a distance of 400 yards.
The IAR6940 rifle fired 2000 rounds without any malfunctions. The shooting modes included single-shot, short bursts, and full-auto sustained fire. The targets were steel targets at distances of 50, 100, 150, and 200 yards.
Due to the IAR6940 rifle’s relatively heavy weight and the grip-style bipod, its shooting accuracy was very high. During short bursts, the IAR6940 rifle exhibited minimal movement. At a distance of 50 yards, it was not difficult to hit the center of the target with 10-20 rounds of long bursts.
At distances of 25-200 yards, hitting targets with 3-5 round bursts was also not difficult. Targets at distances of 250 and 300 yards were also engaged, but the hit rate was lower than for targets within 200 yards.
Subsequently, the IAR6940 rifle’s fire selector was set to semi-automatic mode, and the optical sight was replaced with an ELCAN 4×20mm optical sight, improving the hit rate at 300 yards.
Live fire demonstrated that the IAR6940 rifle could endure 1000 rounds of sustained fire without any malfunctions. In contrast, the M4A1 carbine with a SOCOM heavy barrel experienced a malfunction after firing 870 rounds. This data is already quite impressive for the IAR6940 rifle, which does not use belt feeding and cannot change barrels.
(This article was published in the June 2021 issue of “Light Weapons,” with edits made to the public account)
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