Effective engagement distance can go as far as 120feet.
Beyond that it becomes sketchy because of wind conditions etc... and I've seen an instance where I could'nt hit a guy at 50feet just because of high winds.
Usual engagement distance I've noticed is around 70feet but that all depends on the terrain type.
In a clearing it goes up and in the woods it can go down if it's too ''bushy''.
I've been able to hit man sized targets with my pistol at 200 feet so it's all relative.
If it's a zeroing reference you are looking for, I suggest 70 feet.
Certified Level 2 BA Sniper
Si ton épée est trop courte, allonge la d'un pas. ( Proverbe Hongrois )