I did a lot of play testing on this myself as I was curious what adding gun mods that reduce range was doing to my damage. I can confirm that if you can see a target in your scope, you can hit it. I can also confirm that there is no bullet drop at all, even at the most extreme ranges. Lastly I can confirm that damage drops with range as raiders that normally require one shot to kill will take two or three at extreme range.
How to determine the range of the target … I wish I know. I would have thought the recon scope would have a ‘range’ of target feature also (it really should). Adding that would help considerably with long range attacks.