The 5.56mm NATO round has been the gold standard AR-15 cartridge for well over 60 years. It has been the ammo issued to our frontline soldiers for over a generation and has seen combat on 5 continents in the hands of the U.S. Military and our NATO allies.
The .300 Blackout vs 5.56 debate is one heard at many gun ranges. Which round is superior and do you need to go and get a .300 Blackout AR-15? Ammo.com answers