Interesting question. I sling for distance as opposed to accuracy. In fact, I find that it is easier for me to sling for distance an not accuracy.
I am 65, in reasonable shape. I started slinging in my 60's and will never develop the strength and endurance of a slinger that trained from youth. Also, I do not have access to lead glandes, which, if I understand correctly are aerodynamically efficient. I can consistently sling a golf ball 80 plus yards, in a high arc, similar to a well hit golf ball. It would definitely go over the heads of friendly troops in front of me and then rain down upon the enemies.
Given what I am capable of, I would imagine that a well trained slinger in his teens or twenties could sling 160 yards or more, in a high arc.
You can see my technique here, which relies much more on the efficiency of the sling, than strength.
https://www.youtube.com/watch?v=PqXATejbNlwI hope that this helps.
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