I also was surprised by the 5.56 bullet weights.
Remember Nosler makes a kick ass 64gr and a excellent 77 gr. ..... but remember Noveske makes their "Varmageddon AR " rifle .. which is built around the 55gr Varmageddon ammo
Fitted with top-of-line components and features like the new NSR™ handguard, and Magpul® furniture, as well as a match-grade Noveske barrel, the newly named Varmageddon Rifle cut clover-leaf groups at the range with Nosler Varmageddon Ammunition. Both Nosler and Noveske being Oregon based companies, Leupold® optics out of Portland, Oregon were an easy choice to mount atop this tack-driving rifle. A special VX3® 4.5-14x50mm Long Range Varmageddon edition scope that featured Leupold's recently developed CDS turret system was created to match the trajectory of the 55gr. Varmageddon bullet, providing shooters with dead-on holds to 550 yards.
http://www.nosler.com/varmageddon-ar/