I know this has been properly posted, but I felt like adding a link to this slinging milestone

https://www.amazon.com/Hillfort-Defences-Tactics-Sling-Warfare/dp/178491410X/ref=sr_1_1?ie=UTF8&qid=1501410983&sr=8-1&keywords=Peter+Robertson%2C+Iron+Age+Hillforts+Defences+and+Tactics+os+Sling+Warfare%2C+Archaeopress%2C+9781784914103

Ever been up a hillfort in february, in driving rain, freezing winds and slinging with gloves on - still managed 68% total hit rate :-)

The book is very good. I can't claim to understand half the statistical analysis.
I can tell you that every head shot would have killed.  Didn't see any point doing it, unless I was doing it properly and with feeling :-)

I believe my battle cry was along the lines of: 'take that you scum sucking bastards !'
Pete doesn't mention that - or the fact that he flinched every time I did a warm up throw with an empty sling.

Or that it nearly killed david climbing the hill.

Was good fun, in  a weird kind of way :-)