Hey Badger, Sorry so late on this reply. This seems to be a semi-running thread inIrish folklore.
In the article "Magic Weapons of Celtic Legends" the author quotes
While most sling-balls were naturally shaped stones, some of them
were artificially made and even composed of weird material. Cuchulain
overcomes Foil1 by hurling an iron ball in Foill's " foreheads midst ".4
The blood of toads, hears, and viper.; was mixed with sea-sand and hardened.
j
A ball formed of lime and the brain of the dead champion Mes Gegra,
was kept among the trophies in Emain Macha. One day Cet carries this
ball off ; later he adjusts it in the sling and throws it so that it hit the
crown of Conchobar's head, causing after long illness the death of the
king.6
Magic Weapons in Celtic Legends
E. Ettlinger
Folklore, Vol. 56, No. 3. (Sep., 1945), pp. 295-307.
Marc Adkins
slingbadger wrote on Oct 11
th, 2007 at 12:58pm:
This is a passage from the Cath Finntraga, or the Battle of Ventry. Part of the Fenian cycle of Ireland
"And 2 foreigners were set against them that day. And Conncrither seized his long sided sling ( an tabhaill) and put a straight even stone in it, and gave it a straight well directed cast, so that it went into the forehead of his adversary, and took the brain as a lump of blood out the back of the head."