I think the platform has matured since the 60s, although I understand they don’t like to run when dirty or too lightly lubricated.
They were fine in the 60’s. McNamara’s DOD changed the powder spec for more pressure and it was too dirty and the troops didn’t have cleaning equipment.
Impingement AR 15’s are really dirty weapons and take a long time to clean. That crud gets everywhere and it takes almost an hour to clean after shooting.