Named after the 2nd Battalion 7th Marines, the M27 Infantry Assault Rifle is a rather new addition to the United States Marine Corps arsenal to replace a portion of the M249 light machine guns used by the automatic rifleman.
The M27 Infantry Assault Rifle is the USMC designated for a H&K 416D with an 11" Free Float Rail with a 16.5" barrel, and an ambidextrous charging handle. This firearm is kitted out with a Trigicon SAW Day Optic with 3.5x magnification. The IAR is mostly compatible with 30 Round STANAG magazines and each automatic rifleman is expected to be loaded with up to 27 magazines on hand.
The immediate reaction to this decision by the USMC has very mixed. Some opponents to its adoption feel that it is unwise to go from a belt fed 200 round suppressive fire weapon to a platform that is designed around a 30 round box magazine. Proponents of the change feel that the benefits to having a more reliable, lighter platform outweighs the loss in firepower.
Whether you are for or against the decision it can't be denied that the switch to the M27 IAR means that infantry tactics will need to be altered. Since the 1980's, infantry rifleman tactics involve the use a SAW platform to put direct fire on the target, and going from the M249 to the M27 changes that dynamic. By having a more lightweight platform, the automatic rifleman will be able participate more effectively in urban terrain direct action and thus increasing the effectiveness of a Marine stack. The loss in firepower cannot be denied however, which mean that the conventional suppressive capabilities of the automatic rifleman will be lost.
However, proponents of the M27 IAR argue that having a very accurate weapon will in fact provide a degree of suppressive capability to the automatic rifleman, as accurate shots are just as likely to keep an opponent's head down is a flurry of shots.
The byproduct of the infantry tactics seeing a change means that their training will also need to be updated to accommodate the strengths and weaknesses of the M27. One main advantage regarding training is that the ergonomics of the M27 is very similar to the standard M16A4 and M4A1's currently in use, which means that training for the IAR will be shorter and easier.
The adoption of the M27 IAR started in 2006, when contracts were issued for for various IARs from FN Herstal, H&K, and Colt. So, the decision to go to a 30 round STANAG magazine fed automatic weapon had been decided quite some time ago. This decision in 2006 reflects a shift in the USMC infantry doctrine to turn the marines into a more high speed and maneuverable fighting force.
This doesn't mean that the M249 will not see any use, as nine M249 SAW's will still be kept in each rifle company, but they'll be set up in reserve to be used at each commander's discretion.
How Does this Affect Airsoft?
In reality, this change doesn't affect airsoft tactics much at all. Each airsoft gun is quite capable of accurate suppressive fire with a box magazine capable of holding up to 800 rounds. In a sense, the average airsoft game is very similar to players firing light machine guns at one another. Nonetheless, those interested in replicating a USMC automatic rifleman build will no longer have to invest in a very heavy SAW platform.