What is the maximum effective range of the .308 with subsonic ammo for deer size game?

I tell people to keep their shots within 125 yards..it is a matter of trajectory. Play around on our Ballistics Computer on this website. A subsonic round, whether .22 or .50 cal, will have an extremely curved trajectory. As a rough example, when zeroed at 100 yards, the subsonic will be about 15" low at 150 and 42" low at 200 yds. Since trajectory is a parabolic curve it can be seen that at extended ranges, the projectile is basically falling in like a mortar round. I've kept on an Iron Maiden at Ft. Benning at 350 yards, but if I'd misjudged the range by 10 yards, I'd have missed. The rounds are very consistent, but since wind has a LONG time to act on them, and for the above reason, most folks should keep their shots within 125 yds.