Last year I did a few months on research regarding archeological finds of slings/sling pouches.
The Dublin Slings were particularly hard to track down. In the end a guy working for the National Museum of Ireland sent me photos and details.

As many of the original images are copyrighted, I compiled sketches of all the pouches and labelled dimensions. If you are going to print thrm, the page size is A4.

It's certainly debatable if some of the finds are indeed sling pouches, but up until now dimensions and details have been rather vague. The effects of being buried/preserved on the dimensions are rather minimal in terms of stretch/shrinkage. The information I found suggested a max of 7-13% difference.