I live in south west Michigan where is flat. I am wondering hoe much temp and altitude effect poi. If I sight in my 300rum with a 200gr. accubond and retumbo powder and I dont plan on shooting at an animal past 7or 800 yds. I found a farmer who let me build a dirt mound and now I can shoot to 950yds. I am shooting twice a week 10 rds each day in the 300rum and 40-50 in the 17hmr. I am keeping 5" 10 shot group at 500yds and getting better. I know there is lots of room for improvement but Im still practcing.