The right answer you are looking for is:
http://www.armyproperty.com/nsn/1005-01-368-9852
There was also the RFI sling that usually got hacked up and modified:
http://www.armyproperty.com/nsn/1005-01-541-1771
BFG, Wolf's tail (ETA- yes, the name drives me insane, but there was a crap 2' long sling called that), Magpul, and other slings existed and were used.
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