well being that ur soooooo worried about realism, i'll give it to you straight...if you knew anything about about deep-seeded halo lore, you know that all UNSC soilders get a neural implant upon enlistment, so whenever the soilder touches a weapon, the neural implant sends a crosshair to thier pupil, regular marines in halo see this crosshair, as do ODSTs, as does Master cheif. this is also why soilders can zoom in weapons without a scope. plus, ITS JUST A GAME, CHILL