It is not really an M27. It is actually an HK416, which is an Assault Rifle. I probably would have preferred the HK417, because it looks much cooler.
not its just based off the design of the HK416. it's a separate gun from the hk416. plus the U.S. doesn't use the HK417 only the HK416 by the Marines and special forces basically the HK417 is just a larger version of the HK416.
Weapons like the M4 and the M249 can both fit the role of either an assault rifle or an LMG, but they each fit best in one of those roles and not the other. On the same note, a weapon like the M240B - which is often incorrectly referred to as an LMG in video games - works really well in its intended role as a medium machine gun, but it doesn't work well if used as an LMG.
A weapon can fill multiple roles depending on its design and how it's used. An M27 can function pretty well either as an AR or as an LMG. In fact, in my experience "LMG" is not a term used that much in the military. "Automatic rifle" is more common, at least from what I've seen. The term "LMG" is more popular in video games than anywhere else.
The M27 does a pretty good job of bridging the gap between two weapons categories, unlike any of the other weapons I've mentioned.