My understanding is becase they have not been positively identified as slings, slingbadger is more up on this than I am, based on his work to get the Southampton artifact reclassified.
There are a couple of leather artifacts that have been discovered in Dublin, that may have been slings or maybe not, All that were found was what could possibly be sling pouches.
Here is a private e-mail Badger sent to me when I was collecting information for a class on slinging for a local SCA function
"3 slings have been found from the Fishamble street site in Dublin Ireland. They are currently housed at the national Museum of Ireland in Dublin. They have a distinctive, elongated diamond shape. Dating shows that they are from c. 920-1060 AD. The Museum ID# are E180:7033 E190:6006 E190:7007
Very similar styles have been found in other sites throughout the British Isles In Glouchester, one with decorative holes was associated with a 4th cent. dig. 8 pouches of this design, with slits, have been found at 16-22 Coppergate, in Jorvik (York) These date from the 10-13th cent.
Quita Mold (yes, thats her name) Leather and Leatherworking in Anglo Scandinavian and medieval York York Archeological Trust.
My repro sling on this is 6 inches (15.24 cm) long by 2 wide (5.08 cm). I am not sure if those are the proper measurements, as the pictures had no scale. There are 4 slits on it, "
Going into my Class notes, here is a small portion of what I have
Now another sling design that could have been used is the Cortaillod (La Tene) sling although we only have one picture and a few paragraphs of text on it when it was first discovered. It dates from around (900 BC/BCE)
This is the oldest known european sling. It was excavated at the Cortaillod site near Lake Neuchatel in modern Switzerland around 1875. Unfortuanately this is all we know about this particular sling. The photo above is the only known evidence of it existing.
The actual text reads as follows:
“The cup or what is called the strap, of a sling made of platted flax cords, was found here,and is drawn on the lower part of plate CXXXVIII. This unique specimen will be described in the chapter devoted to the manufactures of flax and bast.”
Once you go to that particulr chapter the text continues;
“Fig. 2 represents one side of what is called the strap of a sling. It was made by plaiting flax cords togather. A portion of the string to which it was attached is shown on the right of the figure (1)”
Footnote 1 yields;
“"Qui fundis ex lino vel setis factis (has enim dicunt esse[?] meliores) contorto circa caput brachio dirigunt saxa-Vegitus De Re Militari Lib iii cap 14-[Tr.]”
Then there are the various Vindolandia artifacts where we have at least one sling pouch, possibly two, that were found near the roman fort in Northern Britian
Marc Adkins
David Morningstar wrote on Mar 28
th, 2009 at 11:20am:
I have done a pretty good net trawl for Irish/Celtic slings and found no reference to surviving artefacts.