The RCO (Rifle Combat Optic) is unfortunately a bastardized version of the real thing, lacking the correct reticle for the RCO and instead using a stripped down version of the TA01NSN crosshair (no range marks, no nightime illumination. The ranging stadia, however, do appear to be properly calibrated on the M16A4 (there is no M4 with an ACOG in the demo, so I haven't checked that).
As you can see, the center crosshair is calibrated to 100m, followed by 200m, 300m, 400m and 500m stadia lines below. The top of the thicker crosshair is 600m. The width of each stadia line (or the width of the thicker vertical crosshair in the case of 600m) corresponds to 19 inches (average width of human shoulders) for the given range. This seems to pretty much work in-game, although the width at 100m is a little off.
Now if we had the proper RCO reticle, this would be immensely useful:http://chemicaldragon.com/yahoo_site_admin/assets/docs/TA31F_ACOG_TRAINING.344110115.ppt
After a little more experimentation in more controlled circumstances in the demo, I observed two things:
1. The distance between the thick horizontal
center crosshairs should be the width of the shoulders at 50m, but this also seems a bit off (sight or the size of an ArmA man, I don't know).
2. I'm beginning to suspect that the reticle is calibrated for the M4 rather than the M16 (as the TA01NSN is in real life). At 500m and 600m the shots seem to group a bit high, but would probably be right on for the M4 (if the difference in velocity is actually taken into account). Maybe someone with the full game can check.