The nylon sling has a problem as it gets worn. They are pretty tight when new, but shortly afterwards, forget it.
In 1973 Rock Island designed a newer sling, I called it soft weave nylon. It is a light OD with plated fittings like the nylon sling. Somewhere in this mess I have the National Stock Number.
Recently the sling was manufactured again, this time with standard parkerized fittings. The webbing is similiar to the black M16 sling in that it is very flexible and will lock tight when used with the sling keeper.