You would expect to see a slinger in 'David & Goliath' but there are many illustrations of medieval slingers such as:
Anglo-Saxon slinger in 'God's Covenant with Abram' from Ælfric's Hexateuch, 2nd quarter of the 11th century (http://warfare2.netai.net/6C-11C/Hexateuch-Cotton_Claudius_B_IV-26v.htm)
Spanish staff-slingers in 'Fighting around Bethulia' from the Roda Bible, c.1050-1100AD (http://warfare2.netai.net/6C-11C/Roda-3-134r-large.htm)
Spanish staff-slingers in 'Army of Antiochus V' from the Roda Bible, c.1050-1100AD (http://warfare2.netai.net/6C-11C/Roda-3-134r-large.htm)
French slinger in 'David and Goliath' from the Bible of Saint Stephen Harding, 1109-1111AD (http://warfare2.netai.net/Medieval/Bible_of_Stephen_Harding-12C-Goliath.htm)
'David and Goliath' from the Melisende Psalter, Jerusalem, 1131-1143AD (http://warfare.atspace.eu/Medieval2/Melisende_Psalter-Upper_Cover-David_and_Goliath-large.htm)
Spanish slinger in 'David and Goliath' from the Biblia Segunde de San Isidoro de Leon, 1162AD (http://warfare.atspace.eu/Medieval2/Biblia_Segunde_de_San_Isidoro_de_Leon-David_Goliath-detail.htm)
English slinger in the 'Life of David' from the Winchester Bible, c.1160–1180AD (http://warfare.atspace.eu/Medieval2/Winchester_Bible-12thC-David.htm)
From Liber ad honorem Augusti by Pietro da Eboli, c.1197
..Sicilian staff-slinger in 'Fighting at Salerno' (http://warfare.atspace.eu/Medieval/Liber_ad_honorem_Augusti-f111r-large.htm)
..Sicilian slinger in 'The people of Salerno attack the palace' (http://warfare.atspace.eu/Medieval/Liber_ad_honorem_Augusti-f116r-large.htm)
..Sicilian slinger in 'Assault by the Salerni on the Terracina Palace' (http://warfare.atspace.eu/Medieval/Liber_ad_honorem_Augusti-f117r-large.htm)
..Sicilian slinger in 'Salerno attacked by the imperial troops' (http://warfare.atspace.eu/Medieval/Liber_ad_honorem_Augusti-f132r-large.htm)
(http://forums.totalwar.org/vb/attachment.php?attachmentid=10910&d=1380445522)
Staff-slingers in the 'Siege of Damietta' from the Chronica Majora by Matthew Paris, 1240–53AD (http://warfare.atspace.eu/Medieval2/Chronica_Majora-Siege_of_Damietta-large.htm)
French slinger in 'David and Goliath' from the Morgan or Maciejowski Bible, mid 13th Century (http://warfare2.netai.net/Medieval/Morgan-Maciejowski-Bible-28v-upper.htm)
French slinger in 'Uriah is Slain' from the Morgan or Maciejowski Bible, mid 13th Century (http://warfare2.netai.net/Medieval/Morgan-Maciejowski-Bible-42r-lower.htm)
The Islamic Defenders of Ciutat de Mallorca, including a staff-slinger, 1285-1290 (http://warfare.atwebpages.com/Franks/Conquesta_de_Mallorca-1285-1290-far_left-Detail_of_top_right.htm)
Druzhina
Illustrations of Costume and Soldiers (http://warfare.atspace.eu/index.htm)
Surprisingly common weapon.
Takes forever to master. Well, it did when I made my own aged ten!
As David is traditionally shieldless, this probably skews down the proportion of slingers depicted with shields.
Ian Heath based his slingers on some of the illuminations above. (http://warfare.atspace.eu/Medieval2/Feudal-39-40-Slingers.htm)
MIRROR SITE
Slingers by Ian Heath (http://warfare.uphero.com/Medieval2/Feudal-39-40-Slingers.htm)
Druzhina
Illustrations of Costume & Soldiers (http://warfare2.netai.net/index.htm)
8)
:D
This picture of David in the Navarre Picture Bible, Pamplona, Spain, 1197AD (http://warfare2.netai.net/Medieval/Navarre_Bible-86.htm) shows some detail of the sling's construction.
MIRROR SITE
David in the Navarre Picture Bible, Pamplona, Spain, 1197AD (http://warfare.likamva.in/Medieval/Navarre_Bible-86.htm)
Druzhina
Illustrations of Costume & Soldiers (http://warfare.atspace.eu/index.htm)