The word "balistrlis = crossbow man" reminded me of the Balearic Isles, probably so named
because the Romans got most if not all of there slingers from there.
Here is a site showing sling and way it was used. I have used a sling, and I think the picture
of throwing underhanded is in error. I swung the sling horizontally, with a sudden acceleration, a
snap of the forearm just prior to letting go of the cord held between thumb and index finger.
The other cord had a loop aroung the middle finger.The effect of the sling is to greatly increase
the length of the arm. Even when an early teenager, I could throw a metal roller bearing from a
wrecked automobile well over a hundred yards. I had a site showing pictures of the missiles the
Calearic slingers used, of molded lead about two inches long, a half inch in diameter, pointed at
both ends, weighing up to two ounces. They have been found in large numbers at old battle sites.
Montesquieu says one of Hannibal's victories over the Romans followed the Roman general's
being hit by a missile from a sling.

From Montesquieu:
Hannibal's light troops were in a different class from those of the Romans. They
were very highly trained and were capable of inflicting much damage on the enemy.
Of particular importance were the Balearic slingers. These were organized into two
corps, each a thousand strong. They were armed with three types of sling for
employment at different ranges. Such was their accuracy and their volume of fire
that they were deemed more useful than archers (pages 23-24).

It is very likely that Hannibal had posted many of his Balearic slingers directly
opposite the Roman cavalry quite deliberately to disrupt both men and horses
(page 80).

The term catapult comes from the Greek word "Katapeltes" "shield piecer" (kata = through,
pelta = small shield"). For a picture of a reconstruction of one, see:
http://www.legionxxiv.org/lrgballistacrew/