>>27675204In the hands of the average joe shooter, 5.56 because most people can't estimate drop of even 5.56 at 600 yards.
The .300blk will have less wind drift and is actually easier to shoot smaller groups at 600m than 5.56, but drops like a mofo so you have to be very good at range estimation/measurement past about 350m (at 350m most 125gr OTM loads, such as Hornady and Remington factory ammo, will have about a 2-foot holdover so POA will be top of head for a CM hit).
.300blk suppresses much better due to having subsonic loads that are both lethal at range and still cycle the gun, as well as expanding subsonic rounds running all-suppressed all-subs all the time is viable.
That being said, 5.56 commercial loads are far cheaper if you're trying to shoot in bulk.
