I remember from the Army BCT gun range in 1969, which I had to memorize over and over, that the maximum effective range of the M-16 was 485 yards, with iron sites.
I don't believe we qualified at more than 300 yards though.
Yep. 500 yard line with open sights is required for basic USMC qualification.
On the 500 line we used the “dog target” (silhouette) so it was easier than the “able” target.
My eyes aren't as good as they were in 1974 but I bet I could still do it.