[quote=@Voltus_Ventus]
<Snipped quote by Kronshi>

Elasticity: You're thinking of a slingshot, the sling David used was braided twine.
Leather: The leather portion of a sling is like 2x2 inches, I have a dagger and I can cut that much out of it without destroying the bag.
I can't make it: It's a matter of poking two holes in the leather square and pushing the twine through.
[/quote]

There's a dead bloke in chain mail next to you right? Unless it's the really expensive kind you can use your dagger to open the rings quite easily. Break out the 2x2 inch piece from that. You can tie the twine to the rings no problem.
should take less time and effort than leather in this situation.