# Colt IAR6940
The **Colt IAR6940** (Infantry Automatic Rifle) is a 5.56×45mm NATO magazine-fed automatic rifle built by [Colt's Manufacturing Company](https://www.edgepedia.org/colts-manufacturing-company) on the M4A1 carbine platform, intended to replace belt-fed light machine guns as a squad support weapon while delivering high volumes of fire in a lightweight package[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf). It was developed for the United States Marine Corps Infantry Automatic Rifle (IAR) competition of 2008, which it lost to [Heckler & Koch](https://www.edgepedia.org/heckler-and-koch)'s M27, but Colt kept it in production, and in 2023 the [Singapore Army](https://www.edgepedia.org/singapore-army) selected it as its new section automatic weapon[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [3](https://www.mindef.gov.sg/news-and-events/latest-releases/27apr23_mq2/).
| Key fact | Detail |
|---|---|
| Role | Squad automatic weapon / light machine gun, magazine-fed, designed to replace belt-fed LMGs[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf) |
| Caliber | 5.56×45mm NATO[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf) |
| Barrel / weight | 16.1 in (40.89 cm) heavy barrel; 9.47 lb (4.3 kg) weapon only[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf) |
| Rate of fire | 700–1,000 rounds per minute[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf) |
| Heat management | Aluminum heat sink integrated with the monolithic rail system, which Colt states extends cook-off time during sustained fire[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf) • [1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) |
| Feed | 30-round detachable magazine standard; compatible with STANAG magazines and drums up to 150 rounds[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf) • [1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) |
| Principal users | Mexican Marines (circa 2010); Singapore Armed Forces (IAR6940E-SG, from 2024)[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle) |
## Origin and the USMC IAR competition
The [United States Marine Corps](https://www.edgepedia.org/united-states-marine-corps) began its Infantry Automatic Rifle program in 2008, seeking a lighter, more maneuverable, and more reliable replacement for the M249 Squad Automatic Weapon in the automatic rifleman role[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/). According to an account of the competition published in *Small Arms Defense Journal*, the Colt proposals were the least expensive at $14 million, against $23.6 million for Heckler & Koch and $27.9 million for FN[5](https://hk-usa.com/wp-content/uploads/2023/09/SADJ_M27-Article-Part-2.pdf).
The competition was won by the HK 416-based design, adopted by the Marine Corps as the M27 IAR[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/). After limited fielding of the M27, the Marine Corps decided in 2011 to replace the M249 SAW in every infantry battalion and light armored reconnaissance battalion, purchasing 6,042 additional H&K rifles with accessories and spare parts at a total cost of $18,430,000[6](https://www.gao.gov/products/b-415261%2Cb-415261.2). Colt nevertheless kept its own IAR6940 as a production item[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/).
## Design
The IAR6940 is built on the M4A1 carbine. It uses the M4A1 lower receiver with a select-fire trigger group allowing single shots and continuous automatic fire, fires from a closed bolt, and retains the standard direct impingement gas operation of the AR-15, M16, and M4 family[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/).
**Heat sink and barrel.** The key difference from a standard M4A1 is a much heavier, thicker 16.1-inch barrel for sustained fire capability, fitted with a massive aluminum heat sink mostly hidden inside the lower handguard, which increases the volume of automatic fire available before overheating[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf). Colt states that the heat sink design significantly exceeds cook-off standards, keeping temperatures lower longer during extended periods of fire[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf). The heavy barrel and heat sink required a heavier H3 buffer with three tungsten weights to prevent bolt carrier bounce in all weather conditions[7](https://smallarmsreview.com/the-colt-iar6940-infantry-automatic-rifle/).
**Receiver and rail.** The upper receiver is of monolithic type, with the handguard integral to the receiver to provide a single long [Picatinny rail](https://www.edgepedia.org/picatinny-rail) at the 3, 6, 9, and 12 o'clock positions; this patented monolithic design is covered by US Patent 7,131,228 B2[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [8](https://thecoltar15resource.com/wp-content/uploads/2019/02/spec-sheet.pdf). The weapon has no standard bipod; supporting accessories attach to a rail in the lower handguard, and it carries a bayonet lug, a feature rarely seen on machine guns[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/).
**Dimensions and performance.** The catalog lists a length of 33.4 inches (84.83 cm) with the stock retracted and 36.72 inches (93.26 cm) extended, a four-position buttstock, folding front sight with removable rear backup iron sight, muzzle velocity up to 3,132 fps (954.63 m/s) depending on ammunition, and a cyclic rate of 700–1,000 rounds per minute[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf).
## Variants
Two other versions of the Colt IAR never progressed beyond the prototype stage: the IAR6940H, with a heat sink, handguard, and backup rear sight designed and manufactured by [Knight's Armament Company](https://www.edgepedia.org/knights-armament-company), and the IAR6940P, an upper receiver with a short-stroke piston instead of the direct impingement gas system[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [7](https://smallarmsreview.com/the-colt-iar6940-infantry-automatic-rifle/). Around 2016 Colt also sold a small number of IAR upper receivers on the civilian market, which can be mounted on compatible semi-automatic or registered select-fire AR-15 type lower receivers[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/).
## Service
Circa 2010 the Mexican Marines bought an undisclosed number of Colt IAR machine guns for units engaged in fighting with drug cartels; after that there was no news of the weapon until the spring of 2023[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/).
**Singapore adoption.** In April 2023 Singapore's Ministry of Defence announced that the Colt Infantry Automatic Rifle 6940 had been assessed as a suitable replacement for the Section Automatic Weapon[3](https://www.mindef.gov.sg/news-and-events/latest-releases/27apr23_mq2/). The selection surprised observers, since the Singapore Army had operated the ST Engineering Ultimax 100 for more than 40 years[4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle). The Defence Science and Technology Agency (DSTA) and the Army evaluated contenders against four criteria: operational effectiveness, reliability, maintenance support, and cost, with firing trials conducted in selected units[4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle).
The Singapore-specific variant, the IAR6940E-SG, was progressively rolled out from April 2024, with all active combat and combat support units equipped and trained by the end of July 2024[9](https://www.dsta.gov.sg/whats-on/spotlight/gunning-for-excellence) • [10](https://defencepioneer.sg/pioneer-articles/17jul24_news1). Singapore's customizations include an ambidextrous charging handle with double latches, an articulated bipod adjustable in angle and length, a built-in deflector so ejected cartridges do not strike left-handed firers, and fire mode selector and magazine release accessible from both sides[4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle) • [10](https://defencepioneer.sg/pioneer-articles/17jul24_news1). In Singapore service the weapon carries a red dot sight paired with a 3x magnifier (identified by Janes as a Trijicon MRO Patrol) and a Steiner DBAL-RL multi-purpose laser aiming device with visible laser, infrared laser, infrared illuminator, and white-light torch modes[4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle).
## By the numbers
The Singapore figures illustrate why the magazine-fed automatic rifle replaced a belt-fed light machine gun there. The IAR6940E-SG has an effective range of 600 m and a cyclic rate of 700–1,000 rounds per minute, against the [Ultimax 100](https://www.edgepedia.org/ultimax-100)'s 460 m maximum effective range and 400–600 rounds per minute[4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle). With the stock retracted the weapon is 85 cm long, 17 percent shorter than the SAW, which improves maneuverability in urban terrain[10](https://defencepioneer.sg/pioneer-articles/17jul24_news1). Unlike the Ultimax 100, the Colt can fire both single rounds in semi-automatic mode and multiple rounds fully automatically, allowing suppressive fire in conventional warfare and targeted shots that minimize collateral damage in urban operations[10](https://defencepioneer.sg/pioneer-articles/17jul24_news1). The heat sink provides better cooling for longer sustained firing[9](https://www.dsta.gov.sg/whats-on/spotlight/gunning-for-excellence).
The trade-off relative to a belt-fed gun is feed capacity: the IAR6940 is fed from 30-round magazines as standard, with 60-round drums used in Singapore service and drums up to 150 rounds compatible, rather than a continuous belt[1](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/) • [4](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle). Colt's stated rationale is that magazine feeding gives commonality of feeding devices to share ammunition with the rest of the squad, while removing the complication of belt-fed systems and their long reloading times[2](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf).
## References
1. [Colt IAR Model 6940 light machine gun (USA), Modern Firearms](https://modernfirearms.net/en/machineguns/u-s-a-machineguns/colt-iar-2/)
2. [Colt 2024 Military and Law Enforcement Catalog, IAR6940E technical data](https://www.colt.com/wp-content/uploads/2024/08/2024-Colt-MLE-Catalogweb.pdf)
3. [Reply to Shephard Media and Jane's Queries on the use of Colt Infantry Automatic Rifle, Singapore Ministry of Defence, 27 April 2023](https://www.mindef.gov.sg/news-and-events/latest-releases/27apr23_mq2/)
4. [Special Report: Singapore gets to grips with new automatic rifle, Janes, 12 August 2024](https://www.janes.com/defence-intelligence-insights/defence-and-national-security-analysis/singapore-gets-to-grips-with-new-automatic-rifle)
5. [The U.S. Marine Corps' M27: Part 2, Small Arms Defense Journal](https://hk-usa.com/wp-content/uploads/2023/09/SADJ_M27-Article-Part-2.pdf)
6. [Matter of FN America, LLC, U.S. Government Accountability Office, B-415261, 12 December 2017](https://www.gao.gov/products/b-415261%2Cb-415261.2)
7. [The Colt IAR6940 (Infantry Automatic Rifle), Small Arms Review](https://smallarmsreview.com/the-colt-iar6940-infantry-automatic-rifle/)
8. [Colt Infantry Automatic Rifle (IAR) Spec Sheet, The Colt AR-15 Resource](https://thecoltar15resource.com/wp-content/uploads/2019/02/spec-sheet.pdf)
9. [Gunning for Excellence, DSTA Spotlight, 17 July 2024](https://www.dsta.gov.sg/whats-on/spotlight/gunning-for-excellence)
10. [SAF equips active combat & combat support units with new light machine gun, Pioneer, 17 July 2024](https://defencepioneer.sg/pioneer-articles/17jul24_news1)
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*Topic: Encyclopedia › Technology and the built world › Engineering and manufacturing › Firearms and ammunition › Machine guns and autocannons*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
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