I heard a discussion about sinpers a month ago. Some said that the number in the ammo bar represents 5 shots, not one. I conducted an expirement, had severel elite snipers trying to take out a squad in the open ground at fairly close range. If the ammo does represent 5 shots, my elite snipers were terrible, every "shot" killed one guy (two on one ocassion). I think it's likely that the bullet went through one guy, and went on to the other. More likely then having missed 4 shots and hit one nearly all the time.
Another reason is, the sinpers usually aim for a while, then use one "shot" (weather it's 5 bullets or one). If every "shot" was 5 bullets, how come he aimed for ten seconds, and then shot five bullets at once? seems more likely it's one carefully aimed shot.