https://www.amazon.co.uk/Hillfort-Defences-Tactics-Sling-Warfare/dp/178491410X/r...As principle slinger in this one - have to recommend it.
First time anyone had ever done proper practical analysis of actual slingers
(as opposed to historians with slings) defending and attacking an iron age hillfort.
Given that most of it was done over 2 days in march where we had: rain. sleet, snow and icey cold winds to contend with while clambering up and down some very deep and steep ditches in wellies. My overall 68% hit rate is pretty good
The statistics are fairly heavy going, but good for all that and currently the only book of it's kind
That and the oceanic one are the only sling specific books I can recall being published recently.