Although perhaps not your grandfather's type of rifle sling. My favortie by FAR is those safari slings:

http://www.cabelas.com/cabelas/en/templates/product/standard-item.jsp?_DARGS=/cabelas/en/common/catalog/item-link.jsp_A&_DAV=MainCatcat20712-cat20776&id=0005803220723a&navCount=3& podId=0005803&parentId=cat20776&masterpath id=&navAction=push&catalogCode=XJ&rid= &parentType=index&indexId=cat20776&has JS=true

can carry the rifle totally hands free. Backpack never gets in the way. And can get the gun up much quicker in case you jump the big boy. Really good when it comes to hiking in rough country.