Begun in July of 2005, the program that produced the IAR (Infantry Automatic Rifle) met or exceeded all of the United States Marine Corps' design requirements for a "lightweight automatic rifle", with a Heckler & Koch variant of the HK416 being selected as the winner in 2009, receiving the type classification of "M27", underlining a desired return to a magazine-fed automatic rifle.
The IAR attempts to hearken back to the heady, halcyon days of the Browning Automatic Rifle (BAR). Weighing in at 19lbs/8.61kg, the .30-06 BAR earned a reputation for reliability on the battlefields of World War 2 and Korea, lasting in combat around the world well into the 1960's. But, with its heavy weight and small ammunition capacity (feeding only from a 20-round magazine), it was recognized that something else was needed.
In 1963, the M14E2/A1 was selected to replace the BAR, in complement to the newly-adopted (1957) M14 rifle. However, serious problems still existed, as the new weapon still relied on a twenty-round magazine, and was much harder to control in fully automatic fire, due to its lighter weight.
As a stopgap, the M60 machine gun was introduced to progressively lower unit levels, both during and after the Vietnam War. A belt-fed weapon firing from an open bolt, the M60 was a dedicated machine gun, rather than a simple automatic rifle. In addition, it was four pounds heavier and could be very temperamental in the field, but was capable of delivering a large volume of accurate automatic fire, assisted by a quick-change barrel, which both the BAR and the M14 lacked.
This "stopgap" solution persisted into the early 1980's, when first the US Army, shortly followed by the US Marines, adopted the 'Minimi' light machine gun, designed by the Belgian firm Fabrique Nationale (which had built designer John Browning's last handgun design, the HP-35 'Hi Power') as the "M249 SAW" (Squad Automatic Weapon).
Firing the same 5.56x45mm cartridge as the M16-series rifles, the belt-fed, quick-change barrel, open-bolt SAW was not the lightest of 'light' machine guns, weighing in at 22lbs/10.5kg when loaded with a 200-round assault pack, and it had its share of teething troubles in its early days, but the worst of these issues were solved fairly quickly. A notable feature of the SAW was its ability to use 30-round M16 magazines (loaded from the lower-left side of the receiver) in the event of the gunner firing all of his belted ammunition in combat.
Ultimately, the troops accepted the weight as a necessary trade-off for the ability to sustain a rate of 100 rounds per minute (rpm) for extended periods, or 200 rpm for short periods. Still, the desire was for the lightest weight possible. While a laudable goal, all weapons involve trade-offs in design; no weapon can be "all things to all men". In 1999, with an aging population of M249's, the Marine Corps began to develop the requirements and criteria for the SAW's replacement.
It is at this point, that something went drastically wrong.
For some reason, despite generations of combat data from war zones around the world, that belt-fed weapons at the lower infantry levels were what won battles, the Marine Corps determined to chart a course to develop a "BAR Lite".
In effect, the HK416/M27 IAR is an attempt to deploy a "5.56mm BAR" at the fire team level. Where the M249 gunner would carry three 200-round assault packs into combat, the IAR gunner has to carry at least twenty-two 30-round M16 magazines to provide the same the same level of fire onto a target -- however, this obscures the facts that a) only 30 rounds at a time can be fired; b) that the effective sustained rate of fire is 30-06 rpm, vs. 100-200 for the SAW; and, c) that the barrel of the M27 is fixed to the weapon and is impossible to change outside of an armorer's shop. Even using H&K's proprietary gas piston system instead of the direct gas impingement operating system of the conventional M16-series, the heat of extended firing will be a critical issue in use, directly impacting squad fire and maneuver.
The IAR's one saving grace - after its lighter weight of eight pounds - is its supposed accuracy. This concept completely misses the point of a fully automatic squad weapon: "accuracy" in automatic weapons is measured by how tight the cone-of-fire and the beaten-zone areas are. Automatic weapons are inherently inaccurate; they are "area of effect" weapons, intended to fire large amounts of ammunition into relatively small areas much faster than conventional rifles. The Marine Corps' Combat Developments and Integration office understands the loss of suppression fire that this represents.
Although reports from Afghanistan indicate positive reception from Marines in the field, the reports of its positive reception read like advertising brochures. If the M27 IAR is as accurate and as much of a quantum shift as it is portrayed to be, then the questions are begged, a) 'Why is the US Army not making any attempt, whatsoever, to adopt this weapon?', and b) 'Why is the M27 not being adopted as the standard infantry rifle?'
While observations have been made that accuracy must be the paramount concern in a counter-insurgency environment, the fact is that the world is changing rapidly, and the possibility of full-on, "main-force" combat with a major power is becoming much more likely than it was even ten years ago. One of the foundational precepts of the post-Vietnam era was that the United States could not afford to be caught at the outset of a war with a military geared to fight the wrong war.
Unfortunately, this is a very expensive proposition in dollars, it is far more expensive in dead troops, lost battles, and wounded and/or disabled veterans. The problems with the M27 IAR, however, go much deeper, as it is not a question of cost: the replacement cost to the US Army of an M249 is currently (FY2011) $4512, while the cost of an M27 is (FY2012) $2896 -- the savings simply are simply not significant enough to warrant the loss of mass-target suppression fire at the squad level.
The real problem is a perfect storm of a flawed design concept, and a civilian leadership bereft of functional knowledge of warfare at the 'muddy boot' level.
Heckler & Koch cannot be blamed for this - they produced precisely the design that was requested, and did it well. There is no doubt that the M27 IAR, like the HK416 that it derives from, is a fine weapon.
But it is not a a replacement for a belt-fed machine gun.