The Hatfield-McCoy Rifles are a pair of dangerous artifacts.
They are a pair of rifles owned by the infamous feuding families. They are connected to each other by a strong gravitational pull; the closer they get to each other, the more powerful said pull is. If they come within firing range, they will both open fire, regardless of if the triggers are pulled.
Looking through the aiming scope of one shows the view of the scope from the other.