For your Wargames Wittering
There's not much evidence of slingers being used as a serious weapon of war, but there is a lot of mention of them being used in the role of hunting or bird scaring. There is one depiction of this in the Bayeux tapestry....but none of them being used in battle.
Typically the staple of children and poor farmers when they are talked about being used outside of hunting/bird scaring it's largely in a 'Christian' context to vanquish a wizard or demon in a "nod" to the bibles David and Goliath.
Most experts seem to think that they were often the only weapon available to some sectors of society when called to war though and combined with the ease of running away when armed only with a sling and bag of bullets would probably have been present on the battlefield. When used it was in the "harassment of the enemy" role, making it difficult for them to form up etc... When faced with the possibility of combat they'd leg it where possible either to hide in terrain, behind the guys with the spears or, most likely go home