How do you get a one hit kill with shot gun on gears of war 2

The shot gun is a great gun if you are close to an enemy. A shot gun is a gun that shoots multiple B.B.'s in one pull of the trigger. That is why the cross hairs (aiming lines) are so big. However they loose power after they travel for a while. With a well placed shot you can explode a locust, or get a head shot... hahahaha