I looked at the ballistics chart and decided to zero the rig for the 180 grain subsonics at 65 metres (I've gone metric because the range finder I use has a metric display). This means, in theory, that the bullet should hit about 3 cm high (about 1.2 inches) at 50 metres (about 55 yards) and I can just aim and shoot out to about 75 metres (around 82 yards). Beyond that the bullet falls rapidly with a drop of maybe five inches at 100 yards.
There was a bit of wind today, but I was pleased to get a 2.5 inch, three shot group at 100 metres (109 yards). I'd be disappointed if I got a group that big with a .223 varmint rifle, but it is cause for rejoicing that I have a cast bullet subsonic load that shoots like that. I believe its best to limit shots at game with this load to 80 yards or so anyway.