Biggest factors are my own abilities,confirmed through shooting,and circumstances,including distance, conditions of wind and terrain,elk location,time of day,etc.
Rifles and loads don't merit much consideration because I won't be there in the first place with a cartridge and bullet that I don't know, for sure, will work. I'm not into "guessing", or finding the lowest common denominator in terminal performance.
Same thoughts here. I do my own load work and shoot the rifles out as far as I can all year round, from on the ground or the actual positions I will get to use in the field. I have a pretty good idea come October how far the rifle in my hands will get it done. Different days (wind) will stop me from taking a shot I could have easily made with no wind.
