I made a sling out of 100ft of 550. I used the double width method. I'm really pleased with how it turned out.
http://www.okshooters.com/forums/showthread.php?t=78386
OK well lets see it because thats what I'm about to do. I think I will be using the dragons tongue and putting a king cobra knot over it so I can take some off if need be and still have a semi wide sling left over.