Re: energy requirements
If its the 7mm you are using, try the 160 Accubonds. You wont be dissapointed in accuracy, wound effects and decent BC's. The LR accuacy is also outstanding. I do admit that I dont know what kind of distance you talking about.
Bullet diameter, bullet weight, velocity, and your maximum range for an elk shot.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.