First off – my eye’s are not what they used to be. 100 yards with a non-magnified optic looks pretty far. 200 yards with a non-magnified optic or open sights is extremely far especially considering target identification. Anyways – back to why I zero my AR at 50 yards.
The M193 55 grain 5.56mm round – and similar loads – are very flat shooting out to 200-250 yards. A lot depends on sight type and distance the sights are above the bore. Typically, with a zero at 50 yards – the bullet will be close to 2 inches high at 100 yards – and 2 inches low at 250 yards. That is pretty flat. My normal shooting distances are between 25 yards and 100 yards – so everything is pretty right on between those ranges.
With my AR’s sighted at 50 yards I feel confident that at any range from 0 – 250 yards – my rifle can hit a torso sized target as long as I have steady aim and good trigger pull.
By the way – my tired eye’s enjoy the view using the Vortex Strikefire sight.