If IIRC from my Army days, the maximum effective range of the A1 was 480 yards.
Well, if I was shooting at a target from 480 yards I would want a different caliber rifle all together.
And I would certainly be kicking myself in the ass for finding myself in a situation where I had to make that shot with anything other than an accurate, scoped platform of .308 or better.
But hitting anything regularly over 300 was a crap-shoot unless it was as big as a small barn.
In my Basic at FLW in ‘70 they had us shooting M-14s the two times we went to the range and shot 350 Yds and up.
I was only so-so with either. Vision issues that I didn’t figure out for another decade. I was pretty good with snap shot “quick-kill” with the BB Gun though...LOL
“M-16 Rifle M16 Training Film: Rifle XM16E1 Operation & Cycle of Functioning pt1-2 1966 US Army 15min “
https://www.youtube.com/watch?v=RKKQcJnMEOo