Yes, the book by Nöldeke. He mentions twice in the book (249, 280) that the sling they used is more similar in shape and functionality to a "lazo", used to throw it over other people, and this was used as a weapon in the Iranian highlands, already mentioned in Herod., 7. 85.

As he used the termini Schlinge and Lazo, I rather suggest that slme kind of loop is involved, like the Cowboy Lasso, wher you can drag the captured individual