5 rifles that almost replaced the M4/M16, and one that did

With the Army's Next Generation Squad Weapon Project, the days of the M4 Carbine and M249 SAW may be numbered. The prototypes from General Dynamics Ordnance and Tactical Systems Inc., Textron Systems, and Sig Sauer are vying to replace both 5.56mm weapon systems in infantry and close-combat units. All three NGSW candidates utilize a 6.8mm round, though their designs and mechanics vary greatly. While the NGSW Project is a departure from the M4/M16 family, it is certainly not the first time that the Army or military in general has attempted to find a new rifle.

The Special Purpose Individual Weapon was an Army program that began in 1951 to develop a flechette-firing rifle. I know what you're thinking: the M16 wasn't even adopted until 1964. So how can the SPIW have been a potential replacement for the M16?

Well, Project SALVO was the Army's first attempt to create the SPIW with the intent of arming soldiers with a weapon that fired small projectiles in large volumes at a high rate of fire, hence its name. Though flechette rounds were tested, the conclusion of Project SALVO was to adopt the Armalite AR-15 as the M16 rifle. However, research and development of the SPIW continued with Project NIBLICK. Now trying to replace the newly adopted M16, the Project NIBLICK also aimed to develop a grenade launcher to complement the flechette-firing rifle. AAI, Springfield Armory, Winchester Arms, and Harrington Richardson all submitted their own unique entries for the SPIW.

Though none of the submissions were deemed to be effective combat weapons, the grenade launcher from the AAI design was further developed and was eventually as the M203 40mm grenade launcher.

Started in 1986, the Advanced Combat Rifle program aimed to replace the M16 with a more accurate rifle. AAI, Colt, HK, Steyr, Ares Inc., and McDonnell Douglas Helicopter Systems all received development contracts, but only the first four companies advanced to the weapon testing phase. The AAI entry utilized a flechette round which, despite the addition of a sound suppressor, created a louder muzzle blast than the M16.

The HK entry was the innovative caseless ammunition G11 which many people will remember from the video game Call of Duty: Black Ops. Steyr submitted a flechette-firing bullpup design that bore a superficial resemblance to the AUG. Colt's ACR prototype was the most conventional, as it was a highly modified version of the existing M16 design with the addition of a new sight, a hydraulic buffer, and a collapsing buttstock. The Colt ACR also utilized an experimental "duplex round", a single cartridge with two small bullets in it, to increase the rifle's volume of fire. However, the "duplex rounds" resulted in decreased accuracy at long range, defeating the purpose of the ACR. In the end, none of the ACR prototypes met or even approached the 100% improvement over the M16 that the program aimed for.

In the aftermath of the ACR program, the Army started the Objective Individual Combat Weapon program. The central idea of the OICW program was to develop an infantry rifle that allowed the user to engage targets behind hard cover with the use of airburst munitions. This idea was refined to combine the airburst, low-velocity cannon with an assault rifle.

The kinetic rounds of the rifle could engage a target directly and, if the target retreated behind cover, the airburst munition could be employed instead. By the early 2000s, contract winner Heckler Koch had resigned the XM29, which featured a 20mm High Explosive Air Bursting launcher and a short-barrel 5.56x45mm NATO rifle. However, the 20mm HEAB was found to be inadequately lethal and the short barrel of the rifle did not generate enough muzzle velocity to be as effective as a standard infantry rifle. The XM29 was also too large and heavy to be carried by a rifleman on the frontlines. The XM29 was shelved in 2004.

Designed by Heckler Koch, the XM8 was an offshoot of the shelved XM29. The grenade launcher part of the project went on to be developed into the XM25 Counter Defilade Target Engagement System. The XM8 was a configurable weapon system that allowed the user to set it up as an infantry rifle, a short-barreled personal defense weapon, and even a bipod-equipped support weapon.

The XM8 also featured an integrated sight and IR laser aiming module/illuminator. Over 200 developmental prototypes were delivered to the military. However, testing yielded numerous complaints including the short battery life of the integrated sight and IR module, ergonomic issues, heavy weight, and a hand guard that would melt after firing too many rounds. Following this first phase of testing, the military requested funding for a large field test, which Congress denied. The project was put on hold in April 2005 and formally canceled on October 31 later that year.

The Individual Carbine competition began in 2010 and sought to replace the M4 carbine in the US Army. The Army solicited manufacturers to submit rifles that provided accurate and reliable firepower, could be fired semi or fully-automatic, possessed integrated Picatinny rails, and was fully ambidextrous. Though the competition did not specify a caliber, any submissions not chambered in 5.56x45mm NATO or 7.62x54mm NATO had to be supplied with ammunition by the manufacturer.

Submissions for the competition included Robinson Armament Co.'s XCR, LWRC's M6A4, Remington's ACR (not to be confused with the ACR program), FN Herstal's FN SCAR, Colt's CM901, Beretta's ARX-160, Adcor Defense's A-556, and HK's HK416, among others. Over the course of testing, some companies backed out after the Army announced that the winner would have to turn over technical data rights to the Army; others dropped out for financial reasons. By Phase II testing, only FN, HK, Remington, Adcor Defense, Beretta, and Colt remained in the running.

Though Phase II was completed, Phase III was halted in 2013 by questions regarding the program's cost and necessity. With M4A1 carbines set to be purchased through 2018, the Army began to rethink carbine acquisition. On June 13, 2013, the Individual Carbine competition was formally cancelled on the grounds that none of the submissions met the minimum scores to continue to the next phase of the evaluation.

The Marines pride themselves on their ingenuity. Their ability to improvise, adapt, and overcome us part of what makes them such a lethal fighting force. The Corps demonstrated this ability with their acquisition and fielding of the M27 Infantry Assault Rifle. In 2006, the Marine Corps issued contracts to manufacturers to replace the M249 Squad Automatic Weapon with a more mobile Infantry Assault Rifle. Submissions included IAR variants of the FN SCAR and HK416 as well as the Colt IAR6940. In 2009, the HK416 won the competition and began a five-month final testing period before it was formally designated as the M27 IAR in the summer of 2010.

In May 2011, General James Amos ordered the replacement of the M249 SAW by the M27 IAR and limited fielding began. Though the 30round magazine-fed M27 could not provide the sustained suppressive fire that the belt-fed M249 SAW could, the M27's increased accuracy and reliability offset the rate of fire. In early 2017, Commandant of the Marine Corps General Robert Neller announced that he wanted to equip every 0311 Marine rifleman with the M27 IAR. To meet this demand, the Corps issued a request for 11,000 M27 IARs from HK. Chris Woodburn, deputy of the Maneuver Branch, Fires and Maneuver Integration at Marine Corps Combat Development Command, said, "The new order will replace all M4s in every infantry squad with an M27, except for the squad leader."

The change would also include Marine infantry training battalions. The deal was finalized in 2018, with the Marines purchasing just over 14,000 M27 IARs. In 2019, the Marine Corps reported that the last of the M27s would be delivered and issued to every infantryman from platoon commander and below by mid-2021. While the M27 will replace the M4 as the standard-issue rifle for the Marine Corps infantry, non-infantry Marines will continue to field the M4 for the foreseeable future. Still, it could be argued that the Marine Corps succeeded in replacing the M4 in a short period of time where the Army failed over a period of decades of programs and competitions. If anything, the NGSW goal of replacing the M4 and M249 with a single weapon system appears to have been lifted from the Marine Corps acquisition and fielding of the M27 IAR.

Only time will tell if the Army will succeed in replacing the M4 through the NGSW Project, or if it be the latest in a long line of failed attempts.