Legionaries with slings

[Frank]

So far all seems good but I can't imagine how legionaries could use slings in their rather tight formation. Each slinger needs considerable room for swinging. Maybe they change their formation accordingly but I am not aware of any historical record of it.

I doubt, they used it during a big battle. At least I never have read something about it. I could imagine, that the last 2 lines went a step back and get the room to use a sling, but that sounds weird, too. However legionairs had more duties than fighting in big battles. In this case, e.g. while patrolling and/or chasing small raids and gangs, the sling might come handy.