SCHOOLBOY,
Let me try to tackle this one for you. You need to have your sling adjusted so that when you shoulder your rifle and take an underhand wrap with your RH for righties, LH for lefties, the rifle is tightly locked in to your shoulder. This will give you a much steadier aiming platform. There are slings out there that are made with rubber and are designed to give you the tightness without taking the wrap, but I don't care for them. Hope this helps.