Trying to help my dad out with his new rifle. He has a fresh out of the box Springfield Saint (5.56, 16"). He is looking for an optic to put on it to "get the most out of the range" I know this means a lot of different things to different people. He has gone further to tell me that he wants to be able to hit human sized targets at 600 yards using 55gr or 62gr factory loads. I don't know if this is possible, so I come to you you all. Most of his actual shooting will happen at 100yd and 200yd targets but he wants to be able to reliably stretch it. With all this in mind, do you have a scope you recommend for his rifle?