Those scopes have what, 1500 range? I know it is further than my Ranger can fire. But the scope isn’t the problem on its own. I dont want to roll over everything. It is the mechanic that you need to be close to fight the MA, but you cannot be close because of the scope.
Stand behind an environment object (tree, rock, hill) and wait until the scope fires. Then quickly shoot it 2 times, and move back behind the cover. After a few hits the scope will point upwards for a while, thats when you can finish it off with melee.