i draw soldiers with helmets as well and these helmets dont have visors. mainly the sight is through camera optics such. so the problem is, why use a scope? i still put them on rifles but i think, why not just put zoom into the optics of the helmet? maybe you can help?
Well, to aim purely with the helmet optics you would need a vectoring device on the rifle to determine its exact position in relation to the helm, and exactly what direction it's pointing in. That in my opinion may be too complex or fragile, and if there is anything off your shots wont be very accurate. You could use an IR laser that your hud locates the end point of, but that can be detected by the enemy, I'm sure in the future at least vehicles will notify the crew when it has been "lased". Any enemy helm with IR detection would be able to see it if not warn of it.
Using a scope with an uplink to the helm could be melded into the view. It would likely provide better magnification and more accurate shots. It is passive, so it isn't detectable by enemy units. Also, if your helm is broken, you can take it off and use the scope manually. You could use a smaller camera device, but you may as well fit a scope for backup use.