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JaegoorA system like that might help with judging a slinger's skill if you had dozens of slingers, which is rare. I don't see where it helps.
the best thing is to sling, then maybe share videos for feedback and then to discuss. The forum's main purpose is to discuss you can't sling in here
why expect more?
100m with pistol is doable(
https://www.youtube.com/watch?v=jJ3XwizTqDw) but modern weapon users seem to prefer direct aiming and shooting ,airgun users might use magnification scopes even for ranges like 30m(!), how more direct can you get?
volley fire at high angles with muskets watch @ 3:41 :
https://www.youtube.com/watch?v=c1Bw-7JzEGAI'd say the use of firearms in short ranges is a matter of preference and convenience it's not easy to find ranges over 100m in cities. If it was available people would do it, same with long range slinging.