The big concept here is Point Blank Range. To put it another way: how far out do you want to shoot a deer without worrying about raising the crosshairs.
I ran the numbers for the new Hornady 160 grain FTX and figured that a 4" target would be reasonable. I also computed based on a scope that's 1.5" off the muzzle.
The numbers were as follows:
If you sight in dead-on at 25 yards you're cool out to 172 yards. That's a little close. That trajectory crosses the 100 yard mark at 2" high, and the 150 yard mark at 1.09" high. The Point Blank Range of this round is 172 yards. That is, it goes no higher or lower than 2" off the point of aim out to 172 yards.
Now, if you take a more conventional bullet, say a 150 grain Hornady FP, will only have a PBR of 161 yards, again sighting in at 2 inches high at 100 yards with a 4" target.
If you were to take the same Hornady FP and zero it dead-on at 100 yards, the bullet would be over 4.5 inches low at 175 yards. The PBR would shift to inside 140 yards.
. . . Or if you were to sight-in dead-on at 50 yards the PBR would shift back to 138 yards.
The thing with Point Blank Range is to figure it out so there are certain sections of the front end of the trajectory that are a bit high, so that you gain the ability to reach out farther.
I use PointBank software. It's a free download. Whenever I cook up a new load, I run it through and calculate the PBR for the load. It usually results in a 2"-high-@100 sighting in. In fact, I've done 30-30, 30-06, 308 WIN and 25-06 loads for deer hunting and they all come out to the same 2"-high-@100.
You can see by the variety of answers that there is no #1 set answer here. Dead-on at 100 for a guy who never takes a deer outside of 100 yards can make sense. Dead-on at 50 does not take that much away from a rifle's reach, and a guy hunting out of a treestand in the woods is not going to know the difference.
