Re: group sizes
I have a safety factor built into the factor I use for determining max distance. I'll shoot no further that which allows a buffer equal to the size of my froups (accuracy). For example, if I can shoot 1 MOA groups at all ranges I take the kill zone size and divide it in half, this gives me the max distance for that critter, deer at 18", half this size in 9" so max range for me and the rifle is 900 yards.
Many folks have reported groups at longer ranges being smaller than their 100 yard groups.