Hi,
as I also continue in researching sling projectiles for my master thesis, I can send you many archaeological and ethnographic articles and my bachelor thesis as well concerning sling and sling balls to broaden up the history of the sling.
I study Prehistoric Archaeology of the Near East at Masaryk University in Brno, in the Czech Republic.
However I would like to ask you for help.
For my master thesis I need you (dear slingers) to fill this questionnaire, the link is here =
http://goo.gl/forms/pkG4Ybi70V.
I think questions could be interesting for you. Please share this that I have as many answers as possible.