Chaperone is the lone shotgun that you have to aim due to it firing a single slug rather than pellets. The big ring that shows up on your screen while you are running around is your shotguns aiming reticle. It also disappears when aiming with a shotgun because shotguns aren't meant to be precise, all you do is point in the general direction of what you want to shoot and fire. For this reason shotguns do not require as much accuracy as a sniper and therefore will never require as much skill to use as a sniper. A sniper is generally shooting at a much smaller target from further away than a shotgun so while Chaperone does require a bit more precision than a standard shotgun its still less than that of a typical sniper. In the case of your standard shotgun you have to aim to activate Rangefinder. If you're telling me that Rangefinder activates on shotguns even when you're not aiming then Bungie might need to take a look at that.