The United States Marine Corps (USMC) has a hard-earned reputation for doing more with less. With relatively small number of boots on the ground and equipment that in some cases dates from generations before, the Corps always acquits itself admirably in whatever theater it is operating. However, even they have to upgrade or modify their equipment from time to time to address changing tactics and battlefield conditions.
When fully loaded with 150 rounds of 5.56mm (shown with optional speedloader), the Saw-Mag weighs in at around 8 pounds. An optional accessory for the Saw-Mag is the loose round speedloader that is designed to load five rounds of 5.56x45mm at a time.
One item in particular that the Corps has been re-examining is the M249 SAW (Squad Automatic Weapon), a proven 5.56x45mm design that offers a great deal of suppressive firepower in a reasonably compact and handy package. However, the USMC recently looked to field a weapon system that could reasonably replicate the performance of the M249, but in a lighter package (that also would be capable of firing from a closed bolt for more accuracy).
The answer was the IAR (Infantry Automatic Rifle) program, which called for a weapons system that combined the firepower of the light machinegun with the accuracy and portability of the assault rifle. The final selection was the M27, a variant of the 5.56mm HK416 from Heckler & Koch.