I've spoke with a lot of them, in fact. Grew up around a bunch of Korean vets.
They fought bravely, were underappreciated, and were overwhelmed by firepower. Manpower = firepower when the manpower is armed.
Most Chinese didn't wear helmets, but your point is well taken. I doubt the average GI could hit a helmet at 300 yards, though, or likely not 200 with iron sights. The rifle just wasn't that accurate, although it was as or more accurate as any of its time. That's why they teach you to shoot center of mass.
Artillery and mortars and airplanes accounted for most of the enemy. They accounted for a lot of Americans, too. I would think very, very few casualties were inflicted by rifle fire at 600 yards by either side. That's artillery range.
The object of a sniper is to get close.
