High velocity is critical to battlesight riflery. Without it soldiers have to make constant range estimations, a skill hard to acquire and even harder to apply when the targets shoot back. On KD ranges one just dials in the right settings on the sight and shoots X rings, but that requires knowing the exact distance -- a reason laser range finders are part of US military sniper team equipment.
The mid range trajectory for current 5.56mm ammo is too high as is, slowing the bullet just makes it worse. Despite a century with smokeless powder the combat engagement ranges haven't changed much, most of it is under 100 meters. This makes a 300 meter battlesight a liability, not an asset.
I'm in favor of this research but they gotta find a way to keep the muzzle velocities up if soldiers are going to hit any thing with the bullets they shoot. 9" high at 175 meters makes it tough to hit targets. Less than 2" high at that range increases hit probability dramatically.
The Hall Study of the early 1950s advocated the abandoment of .30 caliber weapons long before even 7.62mm NATO was adopted. (Gotta admire Hall's research in the pre-computer era, all the charts are hand drawn on graph paper.) Low recoil impulse and flat trajectory make target hits, the reason for this exercise, much more likely. Couple this with a lighter cartridge to allow soldiers to carry many more cartridges and you get an expotential increase in effectiveness.
A 30 round magazine of 77gr cartridges weighs an once more than one with 62gr, so that's a fine trade off, but they gotta get the velocity back up to keep the hit factor high. Currently giving away 500fps on these cartridges.
There's no trajectory issue at 100 meters, but the research is aimed at increasing wounding potential at much, much longer ranges (even though there ain't any targets out there).
-- Chuck